Answer:
Explanation:
The person I sent it to couldn't see it either. I'm going to take a chance and say the Chord (AB) and the Tangent line form a 50 degree angle. If this is incorrect, I won't know, from the diagram, what else to try.
If I'm right then <OAB = 40 degrees because 90 - 50 = 40 because <AOC is a right angle (property of radii and tangents).
<ABO also = 40 (the triangle is isosceles by two legs being radii).
That means that BOA = 180 - 40 - 40 = 100