ΔXYZ is congruent to ΔPQR.
Therefore they have the same dimension on the corresponding parts, and they have the same measurement of angles on the corresponding parts.
∠X = ∠P = 30°
∠Y = ∠Q = ?
∠Z = ∠R = 80°
To find the measurement of ∠Y, use interior angles sum property.
The sum of interior angles on a triangle is equal to 180°
∠Y + ∠X + ∠Z = 180°
plug in the numbers
∠Y + 30° + 80° = 180°
∠Y + 110° = 180°
∠Y = 180° - 110°
∠Y = 70°
The measurement of ∠Y is 70°
The answer is third option
