Answer
f(g(x))=$\frac{3x+9}{7}$-7
g(f(x))=$\frac{3x-4}{7}$
They are not inverses.
Work Step by Step
f(g(x))=3($\frac{x+3}{7}$)-7
f(g(x))=$\frac{3x+9}{7}$-7
g(f(x))=$\frac{(3x-7)+3}{7}$
g(f(x))=$\frac{3x-4}{7}$
They are inverses of each other because f(g(x)) and g(f(x)) are not equal to x.