Answer:
y = 120°
Explanation:
If AC ≅ AD and BC ≅ BD then the shape of the figure is a kite.
Therefore, ∠D ≅ ∠C
Sum of interior angles in a kite = 360°
⇒ ∠A + ∠B + ∠C + ∠D = 360°
⇒ 120° + ∠B + 100° + 100° = 360°
⇒ ∠B = 40°
Sum of interior angles of a triangle = 180°
⇒ ∠B + ∠BDY + ∠y = 180°
⇒ 40° + 20° + ∠y = 180°
⇒ ∠y = 120°