Answer:
214°
Explanation:
The external angle (marked 34°) is equal to half the difference of the arcs ACB and AB.
34° = 1/2(ACB -AB)
Together, the two arcs form a complete circle of 360°, so we have ...
34° = 1/2(ACB -(360° -ACB)) = 1/2(2ACB -360°)
34° = ACB -180° . . . . . . . . . . . . simplify
180° +34° = ACB = 214° . . . . . add 180°
The measure of arc ACB is 214°.