a)
β + β + 110° = 180°
2β + 110° = 180°
2β = 180° - 110°
2β = 70° | : 2
β = 35°
b)
½ * (a + a) * 7 = 28
½ * 2a * 7 = 28
a * 7 = 28 | : 7
a = 4
c)
2α + α = 180°
3α = 180° | : 3
α = 60°
d)
4β + 2β + 210° = 360°
6β + 210° = 360°
6β = 360° - 210°
6β = 150° | : 6
β = 25°