If f(x) = x^4 + 6x, what is the derivative of f(x)?
A) f'(x) = 4x³ + 6
B) f'(x) = 4x³ + 6x
C) f'(x) = 4x³ + 6x + 1
D) f'(x) = 4x³ + 6x - 1