the other equation could be
2y - 6x = -6
Solving:-
y - 3x = -3..........(1)
2y - 6x = -6........(2)
multiplyng the first equation by 2 gives
2y - 6x = -6
so equations (1) and (2) are the same equation
If we graph them they will be the same line
Every point on that line will be a solution.
So there are infinitely many solutions