If you have 12 dollars and you buy 3 paper back books, they each cost the same amount. So you would divide 12 dollars among 3 books to get the same answer for all of them. 12 divided by 3 equals the answer.
Then if you have 28 dollars and you buy 7 paper back books, they all cost the same amount. So that would be 28 divided by 7, equals the same answer.