Answer: We want to know f( g (13) ), here g(13) is just a number, so you are evaluating f in a number, first we need to know the value of g(13). Looking in the diagram you can see that g(13) = 16.
So f(g(13)) = f(16)
Also, looking in the diagram you can see that f(16) = 32
So, f ( g (32) ) = 32
