perhatikan gambar berikut. Besar pelurus sudut QRS ADALAH

180° = 3x° + (5x+20)°
180° = 8x° + 20°
(180 - 20)° = 8x°
160° = 8x°
160/8 = x
20 = x

sudut QRS (5x+20)°
=5(20)+20°
= 100° + 20°
= 120°

3x + 5x + 20 = 180 (Garis Lurus)
8x + 20 = 180
8x = 180 - 20
8x = 160
x = 160 ÷ 8
x = 20

Besar Sudut Pelurus QRS
= 3x
= 3 × 20
= 60°

Jawaban: C