1961 AHSME Problem 32

A regular polygon of n sides is inscribed in a circle of radius R. The area of the polygon is 3R^2. Then n equals:

\textbf{(A)}\ 8\qquad \textbf{(B)}\ 10\qquad \textbf{(C)}\ 12\qquad \textbf{(D)}\ 15\qquad \textbf{(E)}\ 18

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.