You have to use the formula for the slope of a line given two points, in this case from the graph you have the points:
(5,-1) and (-4,2)
The formula is
[tex]m\text{ = }\frac{y1-y2}{x1-x2}[/tex]Substituting the values of y1, y2, x1, x2 we get
[tex]m=\text{ }\frac{-1-2}{5-(-4)}=\frac{-3}{9}=-\frac{1}{3}[/tex]