Answer:
105°
Step-by-step explanation:
The given angles are vertical and congruent , then
8x - 21 = 6x + 3 ( subtract 6x from both sides )
2x - 21 = 3 ( add 21 to both sides )
2x = 24 ( divide both sides by 2 )
x = 12
Then
6x + 3 = 6(12) + 3 = 72 + 3 = 75°
Supplementary angles sum to 180° , thus
supplementary angle = 180° - 75° = 105°
