Let $\displaystyle {A}$ be the area of a circle with radius $\displaystyle {r}$. If $\displaystyle \frac{{{d}{r}}}{{{\left.{d}{t}\right.}}}={3}$, find $\displaystyle \frac{{{d}{A}}}{{{\left.{d}{t}\right.}}}$ when $\displaystyle {r}={4}$.

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