In the figure below, the vertices of triangle RST are on a circle.
 8 in.
 6 in.
 s
 • Line segment TS contains the center of the circle.
 • The perimeter of triangle RST is 24 Inches.
 What is the circle's radius?
 8 inches, because d = 24 – 8 and 2 - 2 = r.
 32 inches, because d = 24 – 8 and 2d=1
 20 inches, because d = 24 - (8 + 6) and 2d =r
 5 inches, because d = 24 - (8 + 6) and d - 2 =r