[tex]\bf \qquad \qquad \textit{direct proportional variation} \\\\ \textit{\underline{y} varies directly with \underline{x}}\qquad \qquad \stackrel{\textit{constant of variation}}{y=\stackrel{\downarrow }{k}x~\hfill } \\\\[-0.35em] \rule{34em}{0.25pt}[/tex]
[tex]\bf \textit{we know that } \begin{cases} y = 36\\ x = -12 \end{cases}\implies 36=k(-12)\implies \cfrac{36}{-12}=k \\\\\\ -3 = k~\hspace{10em}\textit{therefore}~\hspace{10em}\boxed{y=-3k} \\\\\\ \textit{when x = 14, what is \underline{y}?}\qquad y = -3(14)\implies y = -42[/tex]
