Accounting and finance functions QUESTION!!!

QUESTION:

The Sales Day Book for X limited listing the sales made on credit for the month of January 20X1 was as follows:-

SALES DAY BOOK

DATE CUSTOMER Invoice Total Sales VAT
$ $ $

3/1 A Ltd 1,100 1,000 100
5/1 B Ltd 3,300 3000 300
7/1 C Ltd 2,200 2000 200
14/1 D Ltd 3,300 3,000 300

What numbers would be posted to the ledger accounts at the end of January 20X1?

ANSWER ACCORDING TO Kaplan

total invoice total=$14,300 would be posted to Accounts receivable.
Total sales=$13,000 would be posted to the Sales Account.
Total VAT on sales=$1,300 would be posted to the VAT account.

ok so i do understand where each transaction goes to, but I don’t understand where they arrived at these total figures,

someone please explain?