What is the area, in square units, of a circle that has a circumference $12\pi$ units long?

$6\pi$

$12\pi$

$24\pi$

$36\pi$

$144\pi$

Approach

$$ C =2\pi r $$ $$ 12\pi = 2\pi r $$ $$ r = 6 $$ $$ A=\pi r^2 $$ $$ A = \pi (6)^2 $$ $$ = \boxed{36\pi} $$