We have to make sure the functions are simplified into just x to verify that they are inverses. To do this, we have to compose the functions into each other.
f(g(x)) = 4/(4/x)
The 4's cancel out and you're left with just x
f(g(x)) = x
Let's compose f(x) into g(x) now.
g(f(x)) = 4/(4/x)
The 4's cancel out and you're left with just x
Since both functions are equal to x after composing them into each other, we can confirm that they are indeed inverses of each other.