The slope of a line is given by the following expression:
[tex]m=\frac{y_2-y_1}{x_2-x_1}[/tex]
Where m is the slope, (x1,y1) and (x2,y2) are two known points on the line. In this case we have the points (-6, 13) and (8,-29), if we apply them to the expression above and we will be able to find the slope.
[tex]m=\frac{-29-13}{8-(-6)}=\frac{-42}{8+6}=\frac{-42}{14}=-3[/tex]
The slope of the line is equal to -3.
