The term "interior angle" usually refers to the angles found inside a polygon or figure. However, based on the angles you've provided (a = 115°, b = 120°, c = 75°, d = 50°), it seems you're asking whether the setup matches a certain rule or condition, but there isn't enough context to relate them directly.
If you're looking to find the interior angle measure of angle "a", based on the information provided, "interior angle a" is already given as 115°.
Therefore, the measure of interior angle a is:
interior angle a = 115°