From a point on the graph, count down and count right until you get to a another point. For example, for this problem, you can use (0,-2) as a starting point. From here, if you go down 3 and go right 4, you get another point on the graph. So, the slope is -3/4.
A linear equation would be the best fit, but the last point (-1,-7) kinda messes it up. If the -7 would have been a -6 the line y=-2x-8 would fit perfectly.