A line in the horizon meaning a straigh flat line, its counterpart is a vertical line which is up and down. If you look at an x/y line, the x line is the horizon line
Here, I am not sure, try this.
I can't see the options, but you would need to multiply (4x - 2y = 7) by 3, and (3x - 3y = 15) by 4 so that you get 12x in both equations. Then when you subtract, you eliminate 12x. I hope this helps!
