Finding the function inside a composite function?

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!

Re: Finding the function inside a composite function?

Also, the graph of y = kx - 3 intersects the graph of y = x^2 + 8x at two distinct points for?

I set a slider on my CAS and subbed in the options until I found the values, but is there an algebraic method I should use?

Re: Finding the function inside a composite function?

DON't WORRY! I didn't realise that the previous question said that f(x) = 3 / (2x + 1)