Answer:
They are adding up by 12
Step-by-step explanation:
They start at 15, then first add 3, then 6, and then 6 again.
Triangle ABD is i<span>nscribed in circle and </span>has hypotenuse as circle's diameter so angle ABD must be 90°
Since it is parallelogram, ∠ABD = ∠BDC = 90° and it is given that ∠ADB = 30°
So we have ∠CDO = ∠CDB + ∠ADB = 30° + 90° = 120°
Final answers: ∠CDO = 120° and ∠ABD = 90°
