I have -3x + 6y = -12, I can workout how to get to x=0,y=-2,

but I'm lost on the x=3,y=-1/2.

-3x + 6y = -12
6y = 3x -12 (take over the 3x to leave 6y)
y =6/3x - 2 (divide by 6 to get to y)
y = 2x - 2 (final answer)

When I enter x = 3, I get y = 4, not y = -1/2.
as
y = 2x -2 = 6 - 2 = 4

Marcus