3a.
DVA + AVB = 180 (straight line), so
75 + Angle AVB = 180
Angle AVB = 180 - 75
Angle AVB = 105 degrees
3b.
Angle DVC and Angle BVA are vertical angles.
Vertical angles form when we have a geometrical "X".
Vertical angles are equal so,
DVC = BVA
60 = 60
BVA = 60 degrees
3c.
BVC and CVD are in a straight line, so
BVC + CVD = 180
2x + 35 + 3x + 45 = 180
Let's solve for x:
5x + 80 = 180
5x = 100
x = 100/5
x = 20
Angle BVC = 2x + 35 = 2(20) + 35 = 40 + 35 = 75 degrees
Angle CVD = 3x + 45 = 3(20) + 45 = 60 + 45 = 105 degrees