Answer/Step-by-step explanation:
a. Angle y is vertically opposite the angle that measures 80°. Vertically opposite angles are said to be equal to each other, therefore, y = 80°
x + y + 50° = 180° (sum of angles in a ∆)
x + 80° + 50° = 180 (substitution)
x + 130° = 180°
x = 180° - 130° (subtracting 130 from each side)
x = 50°
b. x + 50° = 120° (sum of the 2 opposite interior angles in a ∆ = the exterior angle of the ∆)
x = 120 - 50 (subtracting 50 from each side)
x = 70°
y + x + 50° = 180° (sum of angles in a ∆)
y + 70° + 50 = 180° (substitution)
y + 120° = 180°
y = 180 - 120 (subtracting 120 from each side)
y = 60°