Answer:
C. 20
Step-by-step explanation:
The two marked angles are supplementary, so ...
(5x+12)° +(3x +8)° = 180° . . . . fill in the given expressions
8x +20 = 180 . . . . . . . . . . . . . simplify
8x = 160 . . . . . . . . . . . . . . . . . subtract 20
x = 160/8 . . . . . . . . . . . . . . . . . divide by 8
x = 20
