Javascript questions for review

function exerciseOne(){
  // Exercise One: In this exercise you are given an object called 'mathHelpers'
  // Within mathHelpers, create a method called 'double'
  // This method should take one parameter, a number, 
  // and it should return that number multiplied by two.
  let mathHelpers = {
  mathHelpers.double(*2)
    
  };
  return mathHelpers;
}

function exerciseTwo(userObj){
// Exercise Two: You will be given an object called 'userObj'
// userObject will already have a key on it called 'name'
// Add a method to userObj, called 'greeting'.
// Using the keyword 'this', the greeting method should return the following string:
// 'Hi, my name is ' and the users name.
// eg: If userObj has a name: 'Dan', greeting should return: Hi, my name is Dan'
// NOTE: DO NOT create. a new object.
// NOTE: DO NOT create a key called name the key is already on the object.