Finding the derivative for the following functions

Question

Question:Using the rules of finding derivatives, find the derivative $f’$ of the following functions:

(a) $f(x) = 2x +8$

(b) $f(x) = a + bx + cx^2$

(c) $f(x) = 120$

My answer
I used rules and my answer are these.Does anybody have any comment about my answer?

(a) $f'(x)=2$

(b) $f'(x)=b+2cx$

(c) $f'(x)=0$