You use the process of substitution to solve these problems
2y = 4x + 12 simplify
y = 2x + 6
now why can be plugged into the second equation
2x - (2x + 6) = -6
2x - 2x - 6 = -6
-6 = -6
therefore x is zero
plug it in
2y = 0 + 12
y = 6
what we realize though is
2y = 4x + 12
y = 2x + 6 (multiply by two to receive 2y = 4x + 12)
They are the same graph so there are infinite solutions but plugging in (-4,2) shows it is not a solution.
