3x - y = 6 and y = x - 4, use addition to solve the linear system of equations.

Alright, so I'm trying to figure this out, at first I made y = x - 4 into x - y = 4, then thought I could've gotten it wrong and made it into -x + y = 4. In that one, trying to add the two equations together got me -4x = 2, 2/4 = 0.5 and I already know x = 1 and y = -3, but I just don't understand how to get there?