a)
a+3a+76°=180°
4a=104°:4
a=26°
b)
a+2a+10°+83°=180°
3a+93°=180°
3a=87°:3
a=29°
c)
80°+a+2a+a+10°=360°
4a+90°=360°
4a=270°:4
a=67,5°=67°30
