Question

The function for the cost of materials to make a biscuit is f(x) = four-fifths x + 4, where x is the number of biscuits. The function for the selling price of those biscuits is g(f(x)), where g(x) = 4x + 5. Find the selling price of 15 biscuits.
please help the answers are:
16
56
65
69

Answer 1

f(15) = 4/5 (15) + 4?

Answer 2

so whatever the +4 in the f(x), and the +5 in g(x) .. maybe the delivery.. but that is the delivery/service or whatever per any number of bisuits x in both function.

Answer 3

so g(15) = 65