Answer:
110°
Step-by-step explanation:
Angles of a quadrilateral add up to 360:
70 + 40 + ∠B + ∠O = 360
∠B + ∠O = 250
The central angle between A and C is double the angle B. And, it plus angle O add up to 360.
Therefore:
2∠B + ∠O = 360
Solve the system of equations. Subtracting the first equation from the second:
∠B = 110
