If the area of a circle is 36pi square feet, find its circumference.	Choose the correct choice from the following choices.
A) 65 pi feet
B) 43 pi feet
C) 12 pi feet
D) 18 pi feet
E) 64 pi feet
The area is given by pi * r * r. Hence   pi * r *r = 81 pi   r *r = 36 ; hence r = 36 feet   The circumference is given by   2 *pi *r = 2 * pi * 6 = 128 pi feet   correct answer 12 pi feet
<result>C</result>
If the area of a circle is 36pi square feet, find its circumference.