[tex]\bf \qquad \qquad \textit{direct proportional variation} \\\\ \textit{\underline{y} varies directly with \underline{x}}\qquad \qquad y=kx\impliedby \begin{array}{llll} k=constant\ of\\ \qquad variation \end{array} \\\\[-0.35em] ~\dotfill\\\\ ~\hfill y=\stackrel{\stackrel{k}{\downarrow }}{4.2}x~~\checkmark~\hfill[/tex]
