∠OAC = 27°
Explanation:
When a line is tangent to a circle, the part where the radius meets with the line of tangency will be a right angle. Since we know this, we know that ∠C is equal to 90°. We also know that all of the angles in a triangle will add up to be 180°.
We can now add up the two angles we know and subtract it from 180° to get the measurement of ∠OAC.
∠OAC = 27°