[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}\\\\
-------------------------------[/tex]
[tex]\bf \textit{\underline{s} varies directly with \underline{t}}\qquad s=kt
\\\\\\
\textit{we also know that }
\begin{cases}
s=4.56\\
t=3
\end{cases}\implies 4.56=k3\implies \cfrac{4.56}{3}=k
\\\\\\
1.52=k\qquad therefore\qquad \boxed{s=1.52t}
\\\\\\
\textit{when t = 4.2, what is \underline{s}?}\qquad s=1.52(4.2)[/tex]
