diff --git a/extra/1-currency-conversion.js b/extra/1-currency-conversion.js
index 75b3c6aab..bc797752f 100644
--- a/extra/1-currency-conversion.js
+++ b/extra/1-currency-conversion.js
@@ -5,7 +5,10 @@
   Write a function that converts a price to USD (exchange rate is 1.4 $ to £)
 */
 
-function convertToUSD() {}
+function convertToUSD(priceInGBP) {
+  var priceInUSD = priceInGBP * 1.4;
+  return priceInUSD;
+}
 
 /*
   CURRENCY CONVERSION
@@ -15,7 +18,10 @@ function convertToUSD() {}
   They have also decided that they should add a 1% fee to all foreign transactions, which means you only convert 99% of the £ to BRL.
 */
 
-function convertToBRL() {}
+function convertToBRL(priceInGBP) {
+  var priceInBRL = (priceInGBP * 5.7) * 0.99;
+  return priceInBRL;
+}
 
 /* ======= TESTS - DO NOT MODIFY ===== 
 There are some Tests in this file that will help you work out if your code is working.
diff --git a/extra/2-piping.js b/extra/2-piping.js
index b4f8c4c1b..3941b70ac 100644
--- a/extra/2-piping.js
+++ b/extra/2-piping.js
@@ -16,26 +16,28 @@
   the final result to the variable goodCode
 */
 
-function add() {
-
+function add(a, b) {
+  return a + b;
 }
 
-function multiply() {
-
+function multiply(a, b) {
+  return a * b;
 }
 
-function format() {
-
+function format(format) {
+  var format = "£" + format;
+  return format;
 }
 
 const startingValue = 2;
 
 // Why can this code be seen as bad practice? Comment your answer.
-let badCode =
+let badCode = (startingValue + 10) * 2; return format+badCode;  // because it's hard to read 
 
 /* BETTER PRACTICE */
 
-let goodCode =
+let goodCode = (startingValue + 10) * 2;
+    return format + goodCode;
 
 /* ======= TESTS - DO NOT MODIFY ===== 
 There are some Tests in this file that will help you work out if your code is working.
diff --git a/extra/3-magic-8-ball.js b/extra/3-magic-8-ball.js
index 46f65f928..1fcfb9ccf 100644
--- a/extra/3-magic-8-ball.js
+++ b/extra/3-magic-8-ball.js
@@ -46,7 +46,7 @@
 // This should log "The ball has shaken!"
 // and return the answer.
 function shakeBall() {
-  //Write your code in here
+  console.log("The ball has shaken!");
 }
 
 /* 
@@ -59,7 +59,15 @@ function shakeBall() {
   This function should expect to be called with any value which was returned by the shakeBall function.
 */
 function checkAnswer(answer) {
-  //Write your code in here
+  if (veryPositiveAnswers.includes(answer)) {
+    return "very positive";
+  } else if (positiveAnswers.includes(answer)) {
+    return "positive";
+  } else if (negativeAnswers.includes(answer)) {
+    return "negative";
+  } else if (veryNegativeAnswers.includes(answer)) {
+    return "very negative";
+  }
 }
 
 /* 
diff --git a/mandatory/1-syntax-errors.js b/mandatory/1-syntax-errors.js
index d9e004465..ceb3a7177 100644
--- a/mandatory/1-syntax-errors.js
+++ b/mandatory/1-syntax-errors.js
@@ -1,16 +1,16 @@
 // There are syntax errors in this code - can you fix it to pass the tests?
 
-function addNumbers(a b c) {
+function addNumbers(a ,b ,c) {
   return a + b + c;
 }
 
-function introduceMe(name, age)
-  return `Hello, my {name}` is "and I am $age years old`;
-
+function introduceMe(name, age) {
+  return `Hello, my name is ${name} and I am ${age} years old`;
+}
 function getTotal(a, b) {
-  total = a ++ b;
+  let total = a + b;
 
-  return "The total is total";
+  return `The total is ${total}`;
 }
 
 /* 
diff --git a/mandatory/2-logic-error.js b/mandatory/2-logic-error.js
index 9eb8c8cd7..492621f34 100644
--- a/mandatory/2-logic-error.js
+++ b/mandatory/2-logic-error.js
@@ -1,16 +1,17 @@
 // The syntax for these functions is valid but there are some errors, find them and fix them
 
 function trimWord(word) {
-  return wordtrim();
+  return word.trim();
 }
 
 function getStringLength(word) {
-  return "word".length();
+  let length = word.length
+  return length;
 }
 
 function multiply(a, b, c) {
-  a * b * c;
-  return;
+  let m = a*b*c;
+  return m;
 }
 
 /* 
diff --git a/mandatory/3-function-output.js b/mandatory/3-function-output.js
index 5a953ba60..fae0089cf 100644
--- a/mandatory/3-function-output.js
+++ b/mandatory/3-function-output.js
@@ -1,14 +1,15 @@
-// Add comments to explain what this function does. You're meant to use Google!
+// It generates a random number using Math.random() and it multiplies by 10
 function getRandomNumber() {
   return Math.random() * 10;
 }
 
-// Add comments to explain what this function does. You're meant to use Google!
+// the concat() method is used to merge two or more arrays.
 function combine2Words(word1, word2) {
   return word1.concat(word2);
 }
 
 function concatenate(firstWord, secondWord, thirdWord) {
+  return firstWord.concat(" ", secondWord.concat(" ", thirdWord));
   // Write the body of this function to concatenate three words together.
   // Look at the test case below to understand what this function is expected to return.
 }
diff --git a/mandatory/4-tax.js b/mandatory/4-tax.js
index ba77c7ae2..07f7c520f 100644
--- a/mandatory/4-tax.js
+++ b/mandatory/4-tax.js
@@ -5,7 +5,10 @@
   Sales tax is 20% of the price of the product.
 */
 
-function calculateSalesTax() {}
+function calculateSalesTax(number) {
+  let priceOfProduct = number * 1.2;
+  return priceOfProduct;
+}
 
 /*
   CURRENCY FORMATTING
@@ -17,7 +20,10 @@ function calculateSalesTax() {}
   Remember that the prices must include the sales tax (hint: you already wrote a function for this!)
 */
 
-function addTaxAndFormatCurrency() {}
+function addTaxAndFormatCurrency(pound) {
+  pound = calculateSalesTax(pound);
+  return `£${pound.toFixed(2)}`;
+}
 
 /* 
 ===================================================