Close-- f'(x)=9x^2:

Remember the power rule: where f(x)=x^n, f'(x)=nx^(n-1), repeated for each term. Thus, where f(x)=3x^3 + 6x^0, f'(x)=3*3x^(3-1) + 0*6x^-1 = 9x^2 +0 = 9x^2.

Gotta love calculus, eh? Just finished my homework on one-sided differentials!