The linear equation for two point in plan is:
(x-a)/((y-b) =(x-c)/(y-d) where:
a and b are the coordinates of the first point
c and d are the coordinates of the second point
(r-2)/(y-3) = (r-4)/(y-6)
(r-2)(y-6)=(r-4)(y-3)
-2y=-3r+12-4y
Therefore the equation is:
Y=3r/2