If the line through (-2,4) and (1,y) is perpendicular to one through (-2,4) and (x,2), find the relationship between x and y.
What have you done so far?
The key thing to know is this result: Two lines with slopes $\displaystyle a$ and $\displaystyle c$ are perpendicular, if and only if $\displaystyle ac = -1$, i.e. the product of their slopes is -1.
So see if you can find expressions for the slope of the two lines.