Applying terms in square roots -yeesh

[Parabox]

http://img522.imageshack.us/img522/7522/mat4vj.gif where X is the number into the term http://img524.imageshack.us/img524/2985/prob23ei.gif
Computer F'(6)

The square root is what's giving me my most difficulty. I don't know how to apply the term with a square root and computer f'(6). I've about given up, but it's important to know. Help is needed for this one.

 

[devious_]

Do you know the chain rule?

Think of the general case where $f(x) = \sqrt{ax + b} = (ax+b)^{0.5}$. Now let u=ax+b and apply the chain rule.