A circle has an area of M\:cm^2 and a circumference of N\:cm. If \displaystyle\frac MN=20, what is the radius of the circle, in cm?

**Answer Choices**

A. 10

B. 20

C. 40

D. \frac{1}{10}

E. \frac{1}{20}

A circle has an area of M\:cm^2 and a circumference of N\:cm. If \displaystyle\frac MN=20, what is the radius of the circle, in cm?

**Answer Choices**

A. 10

B. 20

C. 40

D. \frac{1}{10}

E. \frac{1}{20}