Answer: The slope is undefined
Given the following points
A = (6, 1) and B = (6, -9)
slope = rise / run
rise = y2 - y1
run = x2 - x1
Therefore, slope can be written as
slope = y2 - y1 / x2 - x1
from the above points, let x1 = 6, y1 = 1, x2 = 6 and y2 = -9
slope = -9 - 1 / 6 - 6
Slope = -10 / 0
Slope = undefined