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<p>rate of expansion = 3 ft/s</p>

<p>Increase: (C at 3s) - (C at 1s)</p>

<p>Circumference at end of 3rd second = 2pi9
Circumference at end of 1st second = 2pi3</p>

<p>Increase= 2pi9-2pi3 = 2pi(9-3) = 2pi(6) = 12pi</p>