So first let’s put g(f(x)) together by putting f(x) for every x in g(x)
We get g(f(x))=3(3/4x+3)+4 which is the selling price equation
Then you plug in 20 to find the selling price for 20 muffins.
g(f(x))=3(3/4(20)+3)+4
g(f(x))=3(60/4+3)+4
g(f(x))=3(18)+4
g(f(x))=54+4
g(f(x))=58
So the selling price will be $58 for 20 muffins.