A graph of that sort will make a perfectly mirrored "V" shape, and with no offset, the bottom point will be on the y axis. This means that the first equation will intercept the y axis at zero, the second will intercept the y-axis at -15.
"A" may seem correct also, as the second graph will intercept the x-axis at -15, but it is not complete, as it will intercept that axis at +15 as well.
