I can't get anywhere with this question, any help would be awsome:

f(x) = srt(3x+1)

find f'(x) using ONLY the definition of the derivative (no power laws etc)

Starting off:

f'(x) = lim [h->0] [f(x+h) - f(x)]/(h)]

= lim [h->0] [sqt(3x+3h+1) - sqt(3x+1)]/h

From here I cannot seem to get rid of the h from the bottom?