Do you know what the right answer is? I haven't done this stuff since high school. So, I could be wrong. I thought I'd warn you in advance. ;)
I am not sure if this is how you do the problem, but this is how I did it:
I plugged in x-values to each equation until I found the one that fit the graph. The shading I believe represents the side of the line that we would like to have a y-coordinate on. I attached a screenshot of my work. Hope it makes sense!