Question 112727
Let x= the # books that cost $13; and y= the # books that cost $15. 
Set up a system of equations:

x+y=32
13x+15y=458

Solve by subsitution:
x+y=32
y=32-x (plug into second equation)

13x+15(32-x)=458
13x+480-15x=458  -> move x to one side
-2x=-22
x=11  -> (plug into first equation)
11+y=32
y=21

There are 11 books at $13; 21 books at $15

Check:
11*$13=$143
21*$15=$315
=$458