if you notice the graph, the points (0, 6 ) and (1, -2) are on the line, so let's use those then,
[tex]\bf \begin{array}{ccccccccc}
&&x_1&&y_1&&x_2&&y_2\\
% (a,b)
&&(~{{ 0}} &,&{{6}}~)
% (c,d)
&&(~{{ 1}} &,&{{ -2}}~)
\end{array}
\\\\\\
% slope = m
slope = {{ m}}\implies
\cfrac{\stackrel{rise}{{{ y_2}}-{{ y_1}}}}{\stackrel{run}{{{ x_2}}-{{ x_1}}}}\implies \cfrac{-2-6}{1-0}\implies \cfrac{-8}{1}\implies -8[/tex]
