You can
put this solution on YOUR website! .
If to consider your post from the Math point of view then . . .
this part "Solve for x and y" is not relevant to this part "x^2-4x+y^2+6y=12".
And vice versa: This part "x^2-4x+y^2+6y=12" is not relevant to this ""Solve for x and y".
As a consequence, nobody understands you.
Watch your Math language !!