Question

Let f be a differentiable function. If h(x) = (1+f(3x))², which of the following gives a correct process for finding h'(x)?
A) h′(x) = 2(1+f(3x))⋅f′(3x)
B) h′(x) = 2(1+f(3x))⋅f′(x)
C) h′(x) = 2f(3x)⋅f′(x)
D) h′(x) = 2(1+f(3x))⋅3f′(x)