Solve for x. assume that lines which appear to be diameters are actual diameters

11) The sum of the marked angles is 180°.
  65 +10x -5 = 180
  10x = 120
  x = 12 . . . . . selection D

12) The sum of the marked angles is 360°.
  20x +11 +75 +154 = 360
  20x = 120
  x = 6 . . . . . selection C

13) The marked angles are equal.
  9x +5 = 11x -5
  10 = 2x
  x = 5 . . . . . selection D

14) The sum of the marked angles is 180°.
  16x +116 = 180
  16x = 64
  x = 4 . . . . . selection C

The answer is "a"radius = 12.7 unitsdiameter = radius × 212.7 units × 2 = 25.4 units