Step-by-step explanation:
Notice that triangles AOB and BOC are both isosceles triangles, where AO = BO = CO = Radius of the circle.
Angle ABC = 180° - Angle ADC = 180° - 128° = 52° (Opposite angles in a cyclic quad = 180°)
We know that angle OBC = angle OCB = 30°, so
Angle OBA = 52° - 30° = 22°.
Hence, angle BOA = 180° - 2 * 22° = 136°.
