-6x - 2y = 6 add 2y on both sides of the equation

- 6x = 6 + 2y

6 + 2y = - 6x subtract 6 on both sides of the equation

2y = - 6x - 6 and this is exactly the second equation of the system

since the first and the second equation in the system are the same the system has infinitely many solutions.