Because the AC line is tangent to the circle then we have to:
angle C = 90 degrees.
Then, the sum of the angles of a triangle is 180 degrees.
Therefore, we have:
23 + 90 + O = 180
Clearing the angle O we have:
O = 180-90-23
O = 67 degrees
Answer:
the angle O is given by:
O = 67 degrees