just to add some to @DeanR's reply above.
[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]
\rule{34em}{0.25pt} [/tex]
[tex] \bf \stackrel{\textit{\underline{d}istance varies with applied \underline{f}orce}}{d=kf}\qquad \textit{we also know that }
\begin{cases}
f=100\\
d=5
\end{cases}
\\\\\\
5=k100\implies \cfrac{5}{100}=k\implies \cfrac{1}{20}=k~\hspace{8em}\boxed{d=\cfrac{1}{20}f}
\\\\\\
\textit{when f = 360, what is \underline{d}?}\qquad d=\cfrac{1}{20}(360)\implies d=18 [/tex]
