Okay, here we have this:
Let's find (f ∘ g)(4):
(f ∘g)(4)=f(g(4))=f(2)
(f ∘g)(4)=4
Now, let's calculate the value of x when (g∘f)(x)=1:
Considering that (g∘f)(x)=g(f(x))
We can see in the graph that g(x) is equal to 1 in x=1, this mean that:
f(x)=1
Now, of we see in the table we can see that f(x)=1 in x=0.
Therefore finally we obtain that the value of x when (g∘f)(x)=1 is x=0.