The first thing I should do with these two points is find the slope of the line.
m = (y2 - y1)/(x2 - x1)
m = (-1 - 7)/(-9 - -9)
m = -8/0
The slope is undefined. We cannot divide by 0. This makes sense because the points (-9, 7) and (-9, -1) would be right on top of each other. This is a vertical line that has an x-intercept at -9.
Your equation would be x = -9.