[tex]\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 } \\\\ \textit{\underline{x} varies directly with }\underline{z^5}\qquad \qquad \stackrel{\textit{constant of variation}}{x=\stackrel{\downarrow }{k}z^5~\hfill } \\\\[-0.35em] ~\dotfill[/tex]
[tex]\stackrel{\textit{"d" directly proportional to "t"}}{d=kt}\qquad \textit{we also know that} \begin{cases} d=910\\ t=13 \end{cases} \\\\\\ 910=k13\implies \cfrac{910}{13}=k\implies 70=k~\hfill \boxed{d=70t} \\\\\\ \textit{when t=14, what is "d"?}\qquad d=70(14)\implies d=980~miles[/tex]
