Hello Kathy,
You can set proportions as follows:
books 8 10
____ ___ = ____
cost 9.60 x
You can cross-multiply the diagonals from the 2 fractions: 9.60 •10 = 8•x ----> 96 = 8x
Divide both sides by 8 and you get: 12 = x
---> If 8 books cost $9.60, 10 books cost $12.00.
Cheers!