The angles are supplementary which means that (7x-1)+125 = 180 so to go this, simply isolate the variable by doing the opposite operation on the constants to make zero pairs and cancel them out. So 7x-1(+1)+125(-125) makes 7x=185(+1 & -125) which is 61. So then you have 7x=61 and to find x just divide this by both sides to get x about 8.7
