Inside a right circular cone with base radius 5 and height 12 are three congruent spheres each with radius r. Each sphere is tangent to the other two spheres and also tangent to the base and side of the cone. What is r?<spanclass=′latex−bold′>(A)</span>23<spanclass=′latex−bold′>(B)</span>1190−403<spanclass=′latex−bold′>(C)</span>2<spanclass=′latex−bold′>(D)</span>44144−253<spanclass=′latex−bold′>(E)</span>25