Find an equation of the line passing through each of the following pairs of points. (−3, 9), (−3, −5)

To find the equation of the line we will need to find slope and the y-intercept.
 
Given: (-3,9), (-3,-5)
 
What we know:
slope=m=(y2-y1)/(x2-x1)
           m=(-5-9)/9-3-(-3))=-14/0
           m=undefined

When slope=m is undefined we have an a line x=-3. That means that for every y the x value is always -3. This line x=-3 is a vertical line on the graph at -3.