a)
5y+20 +7y+16+10y+5y=2*180
27y+36 =2*180
y=(2*180-36)/27 =12°
b)
y+(180-45) +(180-80) +(180-120) = 2*180
y+180+180+180 -45-80-120=2*180
y+180 -45-80-120=0
y-65=0
y=65°
c)
90+90+7y+2y=2*180
9y=180
y=20°
d)
2*70+2*y =2*180
70+y=180
y=110°
