Answer:
This becomes way easier if you have the knowledge of inverse functions.
Let me make this clear. You have f(x)=x2+1 f(x)=x2+1 and g(f(x))=1/(x2+4)g(f(x))=1/(x2+4). Now pause and think about the second function. The function is defined as g(f(x))g(f(x)), right. now what if there is some way that you could manipulate this function and some how change it to g(x)g(x). Or think about with what other function should you multiply f(x)f(x) [the function in g(f(x))g(f(x)) ] to get xx [so that the function would be g(x)g(x)]. It is f(x)−1f(x)−1 right.
So let us find f(x)f(x) inverse. f(x)=x2+1f(x)=x2+1 then f(x)−1=x−1−−−−−√f(x)−1=x−1 right [ just swipe the xx with f(x)