f(x) = 3 - 4x - x^2 , x < c

g(x) = ln(3-x) , x < 3

I am able to find the composite function and it is

g(f(x)) = ln (3 - (3-4x-x^2)) = ln (4x+x^2)

I understand that g(f(x)) must be greater than 0 and that x cannot be 0 or -4 but how do i find the largest value of c for this composite function?