Question 101218
x = number of cheaper books
y = number of more expensive books
x + y = 15 or y = 15 - x
8.5x + 9.5y =< 135.5
Plug:
8.5x + 9.5(15 - x) =< 135.5
8.5x + 9.5(15 - x) =< 135.5
8.5x + 142.5 - 9.5x =< 135.5
-x =< -7
x >= 7
Atleast 7 books ... least amount being seven