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A stone is dropped into a quiet lake and...

A stone is dropped into a quiet lake and wave move in circles at a speed of 5cm per second. At the instant when the radius of the circular wave is 8 cm, how fast is the enclosed area increasing?

A

`6pi cm^2//s`

B

`8pi cm^2//s`

C

`8/3pi cm^2//s`

D

`80pi cm^2//s`

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