Hello! Finding the rate of change used to really confuse me, but after learning about it a little more I understand it so much better. To find whether a slope line is either negative or positive, you find the lowest point graphed on the line. So, for this example, it would be the point that intercepted the X axis at -8. Then, just follow the line. IF the line leads to a positive quadrant, then the line is positive. IF the line leads to a negative quarderent, then the line is negative. IF the line is a straight line, then it is no change, and if the line is a vertical line with no change it is a change that is undefined.
I hoped this helped in some way, and if you have any further questions feel free to shoot me a message or another question. Good luck :)