A right circular cylinder with its diameter equal to its height is inscribed in a right circular cone. The cone has diameter 10 and altitude 12, and the axes of the cylinder and cone coincide. Find the radius of the cylinder.

**Answer Choices**

A. \dfrac{8}{3}

B. \dfrac{30}{11}

C. 3

D. \dfrac{25}{8}

E. \dfrac{7}{2}