Please help me with these functions ,,,,,,,

Answer:
f(x)= 3x+5 and g(a)= 7
therefore f ( g(a))= 3*g(a)+5= 3*7+5= 26
we know that f (g(x))= x that means that if we put x= a we will have f(g(a))= a
we also calculated above that f(g(a))=26 and f(g(a))= a
then a= 26