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}