You cannot evaluate for (g o f)(0). You will get an undefined answer.
(g o f)(x) tells you to plug in the f(x) function for the x-variable in the g(x) equation; so it would be like saying g(f(x)). This would result in (g o f)(x) = (1/x) - 4. Now plug in 0, (g o f)(0) = 1/0 - 4. One cannot divide by zero in order to simplify the equation and get an answer... unless an undefined answer counts, which I'm pretty sure it doesn't.