ka...tilong jwb soal no 12,13 dan 17 yaaa..tlng yaa

12. 3x + (5x + 20) = 180
8x  = 160
x = 20 

besar ∠QRS = 120°

13. 2x + 3x + 3x + 40 = 360
8x = 320
x = 40

besar ∠COD  = 80°

17. 2 + 3 = 5
 × 180 = 72°
∠b = 72°

∠f = ∠b = 72°
∠g = 180 - 72 = 108°