The function for the cost of materials to make a muffin is f (x) = Three fourths x + 3, where x is the number of muffins. The function for the selling price of those muffins is g (f (x)), where g (x) = 3x + 4. Find the selling price of 20 muffins.

f (x) = 3/4 x+3

g (x) = 3x+4

The new function g (f (x)) will be:

g (f (x)) = 3 (3/4 x + 3) + 4

g (f (x)) = 9/4 x+9 + 4

g (f (x)) = 9/4 x + 13

If x=20; then:

g (f (20)) = (9/4) (20) + 13

g (f (20)) = 45+13

g (f (20)) = 58

Answer: the selling price of 20 muffins will be $58.