Find the angle D of the quadrilateral ABCD inscribed in a circle centered at point O

Find the angle D of the quadrilateral ABCD inscribed in a circle centered at point O, if the angle AOB = 60 and the angle BOC = 50.

So that nothing interferes with the solution of this problem, remember that the central angles are equal to the arc on which they are based, the inscribed angles are equal to half of the arc on which they are supported.
Angle AOB = 60 – central, rests on the arc AB, which means the arc AB = 60.
The angle BОС = 50-central, rests on the arc ВС, which means the arc ВС = 50.
Arc AC = arc AB + arc BC = 60 + 50 = 110.
The inscribed angle D rests on the BC arc, so the angle D = 1/2 * 110 = 55.
Answer: 55 degrees.