[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{cost(c) is directly proportional to price(p)}\qquad c=kp
\\\\\\
\textit{we also know that }
\begin{cases}
p=25\\
c=25.75
\end{cases}\implies 25.75=k25\implies \cfrac{25.75}{25}=k
\\\\\\
1.03=k\qquad thus\qquad \boxed{c=1.03p}\\\\
-------------------------------\\\\
\textit{what's \underline{c} when \underline{p} is 60?}\qquad c=1.03(60)[/tex]
