Answer:
∠ 3 = 105°
Step-by-step explanation:
∠ 1 and ∠ 2 are alternate angles and are congruent , then
8x - 21 = 5x + 15 ( subtract 5x from both sides )
3x - 21 = 15 ( add 21 to both sides )
3x = 36 ( divide both sides by 3 )
x = 12
Then
∠ 1 = 5x + 15 = 5(12) + 15 = 60 + 15 = 75°
∠ 3 and ∠ 1 are same- side interior angles and sum to 180° , then
∠ 3 + 75° = 180° ( subtract 75° from both sides )
∠ 3 = 105°
