this can't be solved without it equaling something
If you mean: y=2x+4 and x+2y=12 => y=-1/2x+6 which means that they are perpendicular to each other.
4x - 2y = 12 divide by 2 both sides 2x - y = 6 subtract 2x to both sides -y = -2x + 6 multiply by -1 to both sides y = 2x - 6 Slope = m = 2, and y-intercept is -6.