the easiest way to find a slope is to use 2 coordinates that the line crosses (preferably whole numbers)
by looking at the graph, we can see that the line passes through (0, -2) & (1, 1)
now the slope equation is simply
[tex] \frac{y2 - y}{x2 - x} [/tex]
after putting the coordinates in, we get..
[tex] \frac{ - 2 - 1}{0 - 1} = \frac{ - 3}{ - 1} = \frac{3}{1} = 3[/tex]
so the slope is 3