Add 12-y to both sides of the second equation to put it into standard form like the first equation:
y +(12 -y) = (x -12) +(12 -y)
12 = x - y . . . simplify
x - y = 12 . . . . second equation in standard form
We see this is identical to the first equation. That means every solution of the first equation is also a solution of the second equation. There are infinitely many solutions.
