3/5÷( 1-3/5)=3/2

Now storybooks belong to other books.

19/3 1÷( 1- 19/3 1)= 19/ 12

Other books are

400 (19/12-3/2) = 4800 (Ben)

There used to be story books.

4800× 3/2 = 7200 (Ben)