To determine the measure of the central angle you have to keep the following properties in mind:
- The measure of the intercepted arc of an angle that has its vertex on the circle is twice the measure of the angle.
-The measure of an angle with a vertex on the center of the circle is equal to the measure of the intercepted arc.
The intercepted arc for both angles is the same so that:
So, you can determine the value of x as follows:

The value of x is 120º