Option : (A)
∠BOC is 90°
So,
∠COD and ∠AOB all should be 90° by linear pair
∠BDC is 50°,
So,
Now as in a parallelogram the opposite sides are equal
We say,
AB parallel to CD
∠DCA = 50°
So,
In triangle COA
∠C = 50° (Stated above)
∠COA = 90° (Proved above)
Therefore,
90° + 50° + x° = 180°
x = 40°