I believe you would need to subtract 55 from 180 (the measure of a straight line) 180 - 55 = 125 125 is your answer
You could also solve by process of elimination A and B can't be the answer as they are less than a 90-degree angle, and MIJ is clearly an obtuse angle (an angle greater than 90-degrees) D can't be the answer as the 305 is greater than a straight angle (180) So C is the only logical answer