from the line, we can pretty much pick any two points to get its slope.
now, let's pick from those already grayed out there hmmm say (-8, 6) and (-2, 0),
[tex]\bf \begin{array}{ccccccccc}
&&x_1&&y_1&&x_2&&y_2\\
% (a,b)
&&(~ -8 &,& 6~)
% (c,d)
&&(~ -2 &,& 0~)
\end{array}
\\\\\\
% slope = m
slope = m\implies
\cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{0-6}{-2-(8)}\implies \cfrac{0-6}{-2+8}\\\\\\ \cfrac{-6}{6}\implies -1[/tex]
