[tex]\bf \qquad \qquad \textit{direct proportional variation}
\\\\
\textit{\underline{x} varies directly with \underline{y}}\qquad \qquad x=ky\impliedby
\begin{array}{llll}
k=constant\ of\\
\qquad variation
\end{array}\\\\
-------------------------------\\\\
\textit{we also know that }
\begin{cases}
x=3.5\\
y=14
\end{cases}\implies 3.5=k14\implies \cfrac{3.5}{14}=k
\\\\\\
\cfrac{1}{4}=k\qquad therefore\qquad \boxed{x=\cfrac{1}{4}y}
\\\\\\
\textit{when y = 18, what is \underline{x}?}\qquad x=\cfrac{1}{4}(18)[/tex]
