Relation between Angle Subtended by an Arc inside & outside the Circle with Angle in Semicircle

Q. Question 9
In the figure, BC is a diameter of the circle and $\angle BAO={60}^{\circ }$. Then, $\angle ADC$ is equal to

(A) ${30}^{\circ }$
(B) ${45}^{\circ }$
(C) ${60}^{\circ }$
(D) ${120}^{\circ }$

Q.

In the picture O is the centre of the circle and A, B, C are points on it. Then $\angle OAC+\angle ABC$ equals ___

1. ${75}^{\circ }$

2. ${90}^{\circ }$

3. ${60}^{\circ }$

4. ${120}^{\circ }$