1) Considering that ∠1 , ∠2, ∠3 are supplementary angles. Hence:
a) 2x +3x+4x =180
9x=180 Dividing both sides by 9
x= 20
b) m∠DBC , If we compare angle 3 and m∠DBC as supplementary too, we can write
m ∠3+m∠DBC= 180º
m∠3 = 180 -m∠DBC
4x = 180 -m∠DBC
80=180-m∠DBC
m∠DBC=180-80
m∠DBC=100º