tolong pake diketahuinya ya...:)

Bab Garis dan Sudut

Diketahui :
∠A = ∠C = 180°
∠B : ∠D = 4 : 5
Misalkan
∠B = 4x
∠D = 5x

Ditanya :
∠B = ... °

Jawab :
∠A + ∠B + ∠C + ∠D = 360°
108 + 4x + 108 + 5x = 360
9x + 216 = 360
9x = 360 - 216
x = 144/9
x = 16

∠B
= 4x
= 4(16)
= 32°