Okay, first we are going to find the slope of the line, using this equation:
We are going to replace with the given points. (6, -1) and (6, -7):
With this we discover that the line is vertical (parallel to the y-axis), this mean that in all cases the solutions are also indeterminate on the Y axis, for that reason Y can take any value for example for x = -3 that corresponds to your first case, and it can take the value that you want to give it, it is indeterminate, You will only see a straight line of solution that goes from -∞ to ∞.
The equation of the line is x=6.