Answer:
The slope is -1/1 or just -1.
(When you need to plot the slope, you use -1/1 to use the strategy Rise/Run or Rise over Run.
If you look at the point (-3,1) From that point, you go down -1 and you run to the side for a positive 1.
Once you do that you'll land at (-2,0) and you can keep on repeating this and you'll see that it lands on the points on the line.
Hope this helps! Please feel free to ask any questions if needed! :)