[tex]\bf \begin{array}{cccccclllll}
\textit{something}&&\textit{varies directly to}&&\textit{something else}\\ \quad \\
\textit{something}&=&{{ \textit{some value}}}&\cdot &\textit{something else}\\ \quad \\
y&=&{{ k}}&\cdot&x
\\
&& y={{ k }}x
\end{array}\\\\
-------------------------------\\\\
thus\implies r=ks\qquad
\begin{cases}
k=2\\
\uparrow \\
constant\ of\\
variation\\
s=4
\end{cases}\implies r=2\cdot 4[/tex]
