A semicircle is inscribed in an isosceles triangle with base 16 and height 15 so that the diameter of the semicircle is contained in the base of the triangle as shown. What is the radius of the semicircle?[asy]
unitsize(0.25cm);
pair A, B, C, O;
A = (-8, 0);
B = (8, 0);
C = (0, 15);
O = (0, 0);draw(arc(O, 120/17, 0, 180));
draw(A--B--C--cycle);
[/asy]<spanclass=′latex−bold′>(A)</span>43<spanclass=′latex−bold′>(B)</span>17120<spanclass=′latex−bold′>(C)</span>10<spanclass=′latex−bold′>(D)</span>2172<spanclass=′latex−bold′>(E)</span>2173