Looking at the right side, 6x + 7 -5x, when you combine like terms you end up with x+7.
Since the first term and the last term, 6x and -5x are like terms you add them. 6 plus -5 is one. In this case it would be x.(it is not necessary to put 1 in front of the x). And 7 is positive and it is the only term left by itself.