Problem 4E

4. The length of a rectangle is increasing at a rate of $8 \mathrm{~cm} / \mathrm{s}$ and its width is increasing at a rate of $3 \mathrm{~cm} / \mathrm{s}$. When the length is $20 \mathrm{~cm}$ and the width is $10 \mathrm{~cm}$, how fast is the area of the rectangle increasing?

 

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