[tex](\stackrel{x_1}{1}~,~\stackrel{y_1}{v})\qquad (\stackrel{x_2}{2}~,~\stackrel{y_2}{10}) \qquad \qquad \stackrel{slope}{m}\implies \cfrac{\stackrel{rise} {\stackrel{y_2}{10}-\stackrel{y1}{v}}}{\underset{run} {\underset{x_2}{2}-\underset{x_1}{1}}}=\stackrel{\stackrel{slope}{\downarrow }}{-8}\implies \cfrac{10-v}{1}=-8 \\\\\\ 10-v=-8\implies -v=-18\implies v=18[/tex]
