The formula to find a slope is y=mx-b where m is the slope (to find the slope you find the change in y and the change in x) which in this case is -3. The change in y is -3 and the change in x is -1. If you put it on a graph the line is going down from left to right and it intersects the y-axis at 18 meaning if you keep sloping down in a straigt line it intersects the x-axis at (6,0).
