Question

A used book store will trade 2 of its books for 3 of yours. If Val brings in 18 books to trade, how many books can she get from the store?

Answer 1

You need to set it up as a fraction and make the fractions equal each other. 
2/3 (2 of their books for 3 of yours)
x/18 (x amount of their books for 18 of yours)
(2/3)=(x/18)
multiply both sides by 18 
and you get 
36/3 which reduces to 12

so your answer is 12

Answer 2

She will get 12 books from the store