Answer
$f(g(x))=f(\frac{1}{3}(x-4))=3(\frac{1}{3}(x-4))+4=(x-4)+4=x$
$g(f(x))=g(3x+4)=\frac{1}{3}((3x+4)-4)\frac{1}{3}3x=x$
There are no values to be excluded.
Work Step by Step
$f(g(x))=f(\frac{1}{3}(x-4))=3(\frac{1}{3}(x-4))+4=(x-4)+4=x$
$g(f(x))=g(3x+4)=\frac{1}{3}((3x+4)-4)\frac{1}{3}3x=x$
There are no values to be excluded.