diff --git a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
index 6deaf61..51a4886 100644
--- a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
@@ -5,18 +5,31 @@
  */
 public class ArrayUtils {
     public static String getMiddleElement(String[] values) {
-        return null;
+        return values[values.length/2];
     }
 
     public static String[] removeMiddleElement(String[] values) {
-        return null;
+
+         String[] result = new String[values.length-1];
+        for (int i = 0; i < values.length/2 ; i++) {
+            result[i] = values[i];
+        }
+        for (int i = values.length/2; i < result.length; i++) {
+            result[i] = values[i+1];
+        }
+        return result;
     }
 
     public static String getLastElement(String[] values) {
-        return null;
+        return values[values.length-1];
     }
 
     public static String[] removeLastElement(String[] values) {
-        return null;
+
+        String[] result = new String[values.length-1];
+        for (int i = 0; i < result.length ; i++) {
+            result[i] = values[i];
+        }
+        return result;
     }
 }
\ No newline at end of file
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java b/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
index 2bf5ec2..3c14690 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
@@ -1,12 +1,27 @@
 package rocks.zipcode.quiz4.collections;
 
+import java.util.HashMap;
 import java.util.Map;
 
 public class WordCounter {
+
+    Map<String, Integer> wordCount = new HashMap<>();
+
+
     public WordCounter(String... strings) {
+
+        for (String word: strings) {
+            if (wordCount.containsKey(word)) {
+                wordCount.put(word, wordCount.get(word) +1);
+            }
+            else {
+                wordCount.put(word, 1);
+            }
+        }
     }
 
     public Map<String, Integer> getWordCountMap() {
-        return null;
+
+        return wordCount;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java
index 199cefc..07ea1eb 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java
@@ -1,4 +1,11 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
-public class Curry {
+public class Curry implements Spice {
+
+    private String name;
+
+    @Override
+    public String getName() {
+        return name;
+    }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java
index e06abbc..0df8ca3 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java
@@ -1,5 +1,7 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
+import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -7,14 +9,33 @@
  * @author leon on 27/12/2018.
  */
 public class Food {
+
+    private List<Spice> spices = new ArrayList<>();
+
+    public Food() {
+        this.spices = spices;
+    }
+
     public List<Spice> getAllSpices() {
-        return null;
+        return spices;
     }
 
     public <SpiceType extends Class<? extends Spice>> Map<SpiceType, Integer> getSpiceCount() {
-        return null;
+
+        Map<SpiceType, Integer> spiceCount = new HashMap<>();
+
+        for (Spice spice: spices) {
+            if (spiceCount.containsKey(spice.getClass())) {
+                spiceCount.put((SpiceType)spice.getClass(), spiceCount.get(spice.getClass()) +1);
+            }
+            else {
+                spiceCount.put((SpiceType)spice.getClass(), 1);
+            }
+        }
+        return spiceCount;
     }
 
     public void applySpice(Spice spice) {
+        spices.add(spice);
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java
index 3c4e177..034ac98 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java
@@ -3,5 +3,12 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Ginger {
+public class Ginger implements Spice {
+
+    private String name;
+
+    @Override
+    public String getName() {
+        return name;
+    }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java
index 4b771a8..8f50a75 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java
@@ -3,5 +3,12 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Pepper {
+public class Pepper implements Spice {
+
+    private String name;
+
+    @Override
+    public String getName() {
+        return name;
+    }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Spice.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Spice.java
index 9ab865b..ed6e324 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Spice.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Spice.java
@@ -4,4 +4,5 @@
  * @author leon on 27/12/2018.
  */
 public interface Spice {
+    public String getName();
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
index 02f2618..fde706b 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
@@ -1,35 +1,46 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import static java.lang.Math.sqrt;
+
 /**
  * @author leon on 21/12/2018.
  */
 public class Calculator {
     public static Double squareRoot(Double value) {
-        return null;
+        return sqrt(value);
     }
 
     public static Double square(Double value) {
-        return null;
+        return value * value;
     }
 
     public static Double[] squareRoots(Double... value) {
-        return null;
+
+        Double[] result = new Double[value.length];
+        for(int i = 0; i < value.length ; i++ )
+            result[i] = Math.sqrt(value[i]);
+
+        return result;
     }
 
     public static Double[] squares(Double... values) {
-        return null;
-    }
 
+        Double[] result = new Double[values.length];
+        for (int i = 0; i < values.length; i++)
+            result[i] = Math.pow(values[i], 2);
+
+        return result;
+    }
     public static Double add(Double value1, Double value2) {
-        return null;
+        return value1 + value2;
     }
 
     public static Double subtract(Double value1, Double value2) {
-        return null;
+        return value1 - value2;
     }
 
 
     public static Double divide(Double divisor, Double dividend) {
-        return null;
+        return divisor / dividend;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
index 5ec61be..bc8c355 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
@@ -1,34 +1,77 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import java.util.Arrays;
+
 /**
  * @author leon on 21/12/2018.
  */
 public class StringUtils {
     public static Character getMiddleCharacter(String string) {
-        return null;
+        return string.charAt(string.length() / 2);
     }
 
     public static String capitalizeMiddleCharacter(String str) {
-        return null;
+        char[] arr = str.toCharArray();
+        int i = arr.length / 2;
+        arr[i] = Character.toUpperCase(arr[i]);
+        String result = new String(arr);
+        return result;
     }
 
     public static String lowerCaseMiddleCharacter(String str) {
-        return null;
+
+        char[] arr = str.toCharArray();
+        int i = arr.length / 2;
+        arr[i] = Character.toLowerCase(arr[i]);
+        String result = new String(arr);
+        return result;
     }
 
     public static Boolean isIsogram(String str) {
-        return null;
+        char arr[] = str.toCharArray();
+        Arrays.sort(arr);
+        for (int i = 0; i < str.length()-1; i++) {
+            if (arr[i] == arr[i+1])
+                return false;
+        }
+        return true;
     }
 
     public static Boolean hasDuplicateConsecutiveCharacters(String str) {
-        return null;
+
+        for (int i = 0; i < str.length() -1; i++) {
+            if (str.charAt(i) == str.charAt(i+1))
+                return true;
+        }
+        return false;
     }
 
     public static String removeConsecutiveDuplicateCharacters(String str) {
-        return null;
-    }
 
-    public static String invertCasing(String str) {
-        return null;
+        StringBuilder result = new StringBuilder();
+
+        for (int i = 0; i < str.length()-1; i++)
+            if (str.charAt(i) == str.charAt(i + 1))
+                i++;
+            else
+                result.append(str.charAt(i));
+            result.append(str.charAt(str.length() - 1));
+            return result.toString();
+
+        }
+
+        public static String invertCasing(String str) {
+
+        StringBuilder result = new StringBuilder(str.length());
+        for (char c : str.toCharArray()) {
+            if(Character.isUpperCase(c)) {
+                c = Character.toLowerCase(c);
+            } else if(Character.isLowerCase(c)) {
+                c = Character.toUpperCase(c);
+            }
+            result.append(c);
+        }
+        return result.toString();
     }
+
 }
\ No newline at end of file
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java
index 40eb4a8..b8206a8 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java
@@ -3,11 +3,15 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Account extends BankAccount {
+public class Account {
+
+    private long id;
+
     public Long getId() {
-        return null;
+        return id;
     }
 
     public void setId(Long id) {
+        this.id = id;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java
index 0dd4183..69cbf3b 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java
@@ -1,17 +1,30 @@
 package rocks.zipcode.quiz4.objectorientation.account;
 
+import java.util.ArrayList;
+import java.util.List;
+
 /**
  * @author leon on 27/12/2018.
  */
 public class Bank {
+
+    private List<BankAccount> accounts;
+
+    public Bank() {
+        this.accounts = new ArrayList<>();
+    }
+
     public BankAccount removeBankAccountByIndex(Integer indexNumber) {
-        return null;
+        BankAccount newAccount = accounts.get(indexNumber);
+        accounts.remove((int)indexNumber);
+        return newAccount;
     }
 
     public void addBankAccount(BankAccount bankAccount) {
+        accounts.add(bankAccount);
     }
 
     public Boolean containsBankAccount(BankAccount bankAccount) {
-        throw new UnsupportedOperationException("Method not yet implemented");
+        return accounts.contains(bankAccount);
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java
index 70ccb74..405a87c 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java
@@ -3,7 +3,34 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class BankAccount {
+public class BankAccount extends Account implements Transactable {
+
+    private double balance;
+
     public void setBalance(Double val) {
+
+        this.balance = val;
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) throws IllegalArgumentException {
+        if (amountToIncreaseBy < 0) {
+            throw new IllegalArgumentException();
+        }
+        balance += amountToIncreaseBy;
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) throws IllegalArgumentException {
+        if (balance < amountToDecreaseBy || amountToDecreaseBy < 0) {
+            throw new IllegalArgumentException();
+        }
+        balance -= amountToDecreaseBy;
+    }
+
+
+    @Override
+    public Double getBalance() {
+        return balance;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java
index 8407f1a..02b991c 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java
@@ -3,18 +3,66 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Employee {
+public class Employee implements Worker, Transactable {
+    private BankAccount bankAccount;
+    private Double hoursWorked;
+    private Double wage;
+
+
     public Employee() {
+        bankAccount = new BankAccount();
+        wage = 35.0;
+        hoursWorked = 0.0;
     }
 
     public Employee(BankAccount bankAccount) {
+        this.bankAccount = bankAccount;
+        this.wage = 35.0;
+        this.hoursWorked = 0.0;
     }
 
     public BankAccount getBankAccount() {
-        return null;
+        return bankAccount;
     }
 
     public void setBankAccount(BankAccount bankAccount) {
+        this.bankAccount = bankAccount;
+
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) {
+        bankAccount.deposit(amountToIncreaseBy);
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) {
+        bankAccount.withdrawal(amountToDecreaseBy);
+    }
+
+    @Override
+    public Double getBalance() {
+        return bankAccount.getBalance();
+    }
+
+    @Override
+    public void increaseHoursWorked(Double numberOfHours) {
+        hoursWorked += numberOfHours;
+
+    }
+
+    @Override
+    public Double getHoursWorked() {
+        return hoursWorked;
+    }
+
+    @Override
+    public Double getHourlyWage() {
+        return wage;
+    }
 
+    @Override
+    public Double getMoneyEarned() {
+        return hoursWorked * wage;
     }
 }