.tolong dibantu ya kk no 3&4

3.a=180°-138°=42°
b=180°-42°=138°
c=180°-138°=42°
4.a.(5x-10°)+(7x-20°)+90°=180°
5x+7x-10°-20°+90° =180°
12x+60° =180°
12x =180°-60°
12x =120°
x =120°:12
x =10°
b.5x-10°=5(10°)-10°
=50°-10°
=40°
c.7x-20°=7(10°)-20°
=70°-20°
=50°