We are asked to solve for the angle of BDC in the figure which is rectangle ACBD.
Since it is a rectangle, each corner has a 90°. Initially, it was given that angle BDA is equal to 50°. Then we can solve for BDC, such as the solution is shown below:
90° = ∠ BDC + ∠ BDA
90° = ∠BDC + 50°
∠BDC = 90° - 50°
∠ BDC = 40°
The answer is 40°.