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
