Let
x -----> the number of books
we have that
the function cost is equal to
C(x)=29,822+11.75x
the money from the sales function is equal to
S(x)=18.25x
equate both equations
18.25x=29,822+11.75x
solve for x
18.25x-11.75x=29,822
6.5x=29,822
x=4,588 books