Real Analysis Problem

I need a correct and concise solution.

The Problem:

f : R --> R , f ' ' ' ' continous.

Prove:

S (from a to b) f (t) dt = [(b - a) / 6] ( f(a) + f(b) + 4 f( (a+b) / 2) )

for all a, b in R.

f ' ' ' ' means four times differentiable.
S means the integral