We can find the approximate measurement of angle ABC and it is equal to 180°. The summation of all angles in a triangle is 180°.
Solving for x or angle B, we need to used Pythagorean theorem and SOH CAH TOA.
Solving for angle A:
sinA = 10.5/20
A = 31.67°
Solving for angle B:
180° = ∠C + ∠B + ∠A
180° = 90° + ∠B + 31.67
∠B = 58.33°
The x value is 58.33°.