so hmm check the picture below
[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\\
variation
\end{array}\\\\
-------------------------------\\\\
\textit{we know that }
\begin{cases}
x=3\\
y=1
\end{cases}\implies 1=k3\implies \cfrac{1}{3}=k
\\\\\\
thus\qquad \qquad y=\cfrac{1}{3}x[/tex]
