Let g:R \{-13/4 }-->R be another function with f[g(x)] = 3 / (4x + 13). Find the rule of g(x). How should I do this? D:

Also,

The function f satisfies the functional equation f[f(x)] = x for the maximal domain of f. The rule for the function is?

All help is appreciated and I can't turn bold off!