There is no question context so it is not sufficient for an answer, however I am assuming its asking for you based on the images to pair the charts to graph.
First lets find the slope of (20,-1) (21,-1.5)
[tex]Slope = \frac{y2-y1}{x2-x1}[/tex]
-1+1.5
20-21
The slope for that chart is 0.5/-1 which is -0.5 or -1/2. This makes that chart paired with the following graph:
