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A balloon's radius grows 3 cm/s. How quickly does its surface area increase at r = 4 cm?
A48π cm²/s
B24π cm²/s
C32π cm²/s
D96π cm²/s
Answer & Solution
Correct answer: D. 96π cm²/s
S = 4πr² gives dS/dt = 8πr(dr/dt) = 8π × 4 × 3 = 96π cm²/s.
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