55.
The only type of line with undefined slope is a vertical line.
In a vertical line, all points have the same x-coordinate.
The general equation of a vertical line is x = k, where k is the x-coordinate of all points on the line. If you are given one point, then you know the x-coordinate of that point, but since all points have the same x-coordinate, you also know the x-coordinate of all points.
Equation is: x = -6
56.
Same explanation as above.
x = 2