g(f(2)) means work out whatever f(2) is then plug this into g(x).
So f(2) is 3 because we just find the x-value 2 in the left hand column and read across. This is 3.
So then we find g(3) by finding the x-value 3 in the left hand column and read across. This is 10.
So g(f(2)) = 10
