f(x) and g(x) are inverse functions when the following equations are true:f(g(x))=x
g(f(x))=xTo find (f(g)(x)) or (g(f(x)), use the inner function as the input for the outer function.
f(g(x))=-3((-x/3-2))-6 = x
g(f(x))= (-(-3x-6)/3)-2 = x, hence f and g are inverse functions