Ok, so now that I reread this question, I can give you that answer.
First, graph a line of which passes through -2,-2, and -8. I believe they can be either x or y coordinates If not, plz correct me. This will give you a line that goes down as shown in the picture. Now what you do is that you count how many times up it takes you to get to the next plot and how many times you go left. Your slope will come out to be -4