tolong jawabin dong '-'

1)
a)
3b+b = 180°
4b = 180°
b = 180°/4
b = 45°

b) ∠ABC = 180°

c) ∠DBC = b = 45°

2)
a)
2x - 30° + 40° = 180°
2x + 10° = 180°
2x = 180°-10°
2x = 170°
x = 170°/2
x = 85°

2)
∠ROQ = 2x-30°
= 2. 85°-30°
= 170-30
= 140°