For 50°, answer is 65°
For 90°, answer is 45°
For 150°, answer is 15°
A linear pair of angles adds up to 180° by definition. So the new angle drawn by the ray will have an angle of 180°-a where a is the measure of the original angle. And the bisector of that new angle will be (180°-a)/2. So with that in mind, let's calculate the new measures of the described construction.
50°: (18° - 50°)/2 = 130°/2 = 65°
90°: (180° - 90°)/2 = 90°/2 = 45°
150°: (180° - 150°)/2 = 30°/2 =15°
