Find g for f(g(x)) = 5 + x when f(x) = x^2 + 3

Does anyone know how to find g?

I tried the following:

sqrt(x) results in x + 3 which is wrong...

sqrt(x) + 2 results in x + 4sqrt(x) + 7 which is wrong...

etc...

Nothing seems to work.... How do I do this? Please help!