The circumference of a particular circle is 18 cm. In square centimeters, what is the area of the circle? Express your answer as a common fraction in terms of $\pi$.
If r is the radius of the circle, then the circumference is 2πr. Setting 2π r equal to 18 cm, we find r=9/π cm. The area of the circle is πr^2= π (9/π)^2 = 81/π square centimeters.
