[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}\\\\ \stackrel{\textit{"u" varies directly with "v"}}{u=kv}\qquad \textit{we know that } \begin{cases} k=0.6\\ v=7.8 \end{cases} \\\\\\ u=(0.6)(7.8)\implies u=4.68[/tex]
