Answer: The angle is 90 degrees.
Explanation:
A triangle that has a diameter as its hypotenuse inside a inscribed circle has a right angle opposite of its hypotenuse. This is true for any right triangle inscribed in a circle, because the equation to get measure B is:
(angle ABC) = 1/2 * (angle AOC)
Angle AOC is 180 degrees. Putting 180 into the euqation, we get 90 degrees for angle ABC.