a perpendicular line has the slope of the line that it's perpendicular but its the negative reciprocal of it. So for ex: line 1 = 2x then the line perpendicular to it is -1/2x.
In this case, the slope is 3x. The line perpendicular to it therefore, should be -1/3x.
The problem states the line has the same y-intercept so it has to still be -r.
So the equation of the line perpendicular to y=3x-r with the same y-intercept is y=-(1/3)x -r
