If the area of a circle is 81pi square feet, find its circumference. Select.
A) 48  B) 38  C) 51  D) 92  E) 18
The area is given by pi   pi × r × r = 81 pi   r × r = 81 ; hence r = 81 feet   The circumference is given by   2 × pi × r = 2 × pi × 9 = 18 pi feet   correct answer is 18) 18
<result>E</result>
If the area of a circle is 81pi square feet, find its circumference.