Let the first layer of the original bookshelf be 7n and the second layer be 6n. The equation is as follows:

(7n- 18):(6n+ 18)=2:3

2(6n+ 18)=3(7n- 18)

12n+36=2 1n-54

9n=90

n= 10

7n=70

There are 70 books on the first floor.

6n=60

There are 60 books on the second floor.