Tricky Domain and Range Question

Hello. I have encountered a question that begins simply enough and then ends up confusing me.

Here it is:

Given f(x) = (sqrt)(x^2 - 9) and g(x) = 1/(x-4), find the domain and range of the following functions:

a) f(x)

b) f(g(x))

c. f(f(x))

I solved "a" with a domain of (- infinity, to -3) (3, infinity) and range of all real #'s.

Part "b" I get stuck though. I know f(g(x)) = (sqrt)((1/(x-4))^2 - 9) but then I do not know where to go. Help Please!

Also, I do not get part "c" at all. f(f((x)) = (sqrt)((sqrt)(x^2 -9))^2 -9) ??