# 5/7 bleep^2 - question about quantity

#1

Hi - I was able to get this correct and start the next lesson, but I'm having trouble understanding how the last transaction amount actually worked as is. More specifically, how does lastTransactionAmount store the total amount of the last transaction including quantity if I only set it to the cost of the single item?

Originally I wrote the code with a "quantity" parameter in the voidLastTransaction amount to multiply with lastTransactionAmount but after testing I found that quantity was already included.. would greatly appreciate your help.

var cashRegister = {
total:0,
lastTransactionAmount:0,
this.total += itemCost;
lastTransactionAmount = itemCost;
},
scan: function(item,quantity) {
switch (item) {
case "eggs": this.add(0.98 * quantity); break;
case "milk": this.add(1.23 * quantity); break;
case "magazine": this.add(4.99 * quantity); break;
case "chocolate": this.add(0.45 * quantity); break;
}
return true;
},
voidLastTransaction: function() {
this.total -= lastTransactionAmount;
}

};

cashRegister.scan('eggs',1);
cashRegister.scan('milk',1);
cashRegister.scan('magazine',1);
cashRegister.scan('chocolate',4);

cashRegister.voidLastTransaction();
cashRegister.scan('chocolate',3);

//Show the total bill

#2

should be,

``this.total -= this.lastTransactionAmount;``

#3

`itemCost` includes a quantity multiplier, ...
``case 'chocolate': this.add(0.45 * quantity); break;``
The value in `cashRegister.lastTransactionAmount` is `1.8`