Ty D. answered 10/24/18
Educator with 10+ years of experience from K-12
It helps if you sketch out this problem. When you draw all three lines you'll see a triangle with one side on the y-axis (x=0) and two intersecting lines, one that starts at (0,-5) represented by y=2x -5, and the other that starts at (0,9) representing y = mx + 9.
We have to use the fact that this is a right triangle, which means y = mx+9 would have to represent a horizontal line with m=0 for the slope, so y = 9.
I don't believe that there is another way to draw this right triangle, as the y-intercept is fixed at (0,9) for the y = mx + 9.