You are aware that are you not? So the two given points are and . Since the x coordinates are the same, the line is vertical. Any line perpendicular to it is horizontal and so has 0 slope.
The fact that a line "does not have a slope" does not mean a line perpendicular to is does not. Again, the fact that you were unable to calculate a slope for this line means it is vertical and so a line perpendicular to it is horizontal.
(I would not say "division by 0 does not count". I would say "we cannot divide by 0 so this line has NO slope- which means it is vertical". And please use [ tex ] and [ /tex ] tags.)