to get the slope of any straight line, we can simply use two points off of it, hmmm say let's use here (2,8) and (4,4)
[tex]\bf (\stackrel{x_1}{2}~,~\stackrel{y_1}{8})\qquad
(\stackrel{x_2}{4}~,~\stackrel{y_2}{4})
\\\\\\
slope = m\implies
\cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{4-8}{4-2}\implies \cfrac{-4}{2}\implies -2[/tex]
