add 50+72 and it will give you 122 and the triangle should be uhhh hang on gosh this is hard to remember, um 180 I believe so if you do 180-122 it will give you 58. Now you do 180 -58 because of the °180 line and I believe and it will give you 122 for the missing x but don't take my word on it cause I'm not sure if it's right but that's what I remember