You can use the slope equation (m = slope):
[tex]m = \frac{y_2-y_1}{x_2-x_1} [/tex]
Plug in the numbers:
[tex]m= \frac{3-0}{-13-(-10)} = \frac{3}{-13+10} = -\frac{3}{3} = -1[/tex]
So, the slope of the line that passes through (-10, 0) and (-13, 3) is -1.