Answer:
120°
Step-by-step explanation:
The arc ABC is twice that of the angle created at D. This is the central angle theorem extension.
So we can say that arc ABC = 2* 120 = 240
We know total circle angle is 360 degrees so, arc ADC + arc ABC = 360
Hence,
arc ADC + 240 = 360
arc ADC = 360 - 240 = 120
