## Calculus (3rd Edition)

According to the chain rule, $\frac{d}{dx}(f(g(x)))=f'(g(x))\times g'(x)$ When $x=6$, $\frac{d}{dx}(f(g(x)))=f'(g(6))\times g'(6)$ $=f'(6)\times3=4\times3=12$