Any time you have an undefined slope the line will be a vertical line.
The equation for vertical lines are always x= #. The # is the x value of the ordered pair. If you don't have an ordered pair but have a picture, it will be the value of the x-intercept (the point where the line crosses the x-axis).
For your set of ordered pairs (3/8, 1) the x-value is 3/8 so the equation
is x = (3/8)