$\begin{align}  & y=3\sin (-4x) \\ & \text{Using chain rule method, let }u=-4x \\ & y=3\sin u \\ & \frac{dy}{du}=3\cos u,\text{   }\frac{du}{dx}=-4 \\ & \frac{dy}{dx}=\frac{dy}{du}\times \frac{du}{dx}=3\cos u\times (-4)=-12\cos u \\ & \frac{dy}{dx}=-12\cos (-4x) \\\end{align}$