Consider the functions f(x) = x to the second power + 9x and g(x) =1/x.
f(g(-1)) is?
g(f(1/2)) is?

Let's first calculate the inner functions, then fill in in the outer one:

g(-1) = 1/-1 = -1.
f(-1) = (-1)^2 + 9(-1) = 1 - 9 = -8

And then 

f(1/2) = (1/2)^2 + 9(1/2) = 1/4 + 9/2 = 19/4
g(19/4) = 4/19