Jon P. answered 05/27/15
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The rest is just calculating -- presumably on a calculator. Multiply 210 times π (most calculators have a specific button for π, or you can use 3.14159) and round to the nearest integer, and you get 660 feet.

Jon P.
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You're welcome. The trick (not really a trick) was just to realize that π is just a number, no more algebra needed!
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05/27/15
Jared N.
05/27/15