Person.js

function Person(first,last,age) {
   this.firstname = first;
   this.lastname = last;
   this.age = age;
   var bankBalance = 7500;

   var returnBalance = function() {
      return bankBalance;
   };

   // create the new function here
    this.askTeller = function() {
        return this.returnBalance;
    };
}

var john = new Person('John','Smith',30);
console.log(john.askTeller());
console.log(john.returnBalance);
var myBalanceMethod = john.askTeller();
var myBalance = myBalanceMethod();
console.log(myBalance);