so.. traveling without the wind, let's say the pedalist has a speed of "r"
with the wind, the wind's rate is added to it, so, he's not going "r" fast, he's really going r+3 fast
against the wind, he's going r - 3 fast
notice, he covers 30 miles with it, and 18 miles against BUT the time for both ways is the same, say time "t"
now, recall your d = rt, distance = rate * time
thus [tex]\bf \begin{array}{lccclll}
&distance(mi)&rate(mph)&time\\
&-----&-----&-----\\
\textit{with the wind}&30&r+3&t\\
\textit{against the wind}&18&r-3&t
\end{array}\\\\
-----------------------------\\\\
\begin{cases}
30=(r+3)t\implies \frac{30}{r+3}=t\\\\
18=(r-3)t\implies \frac{18}{r-3}=t
\end{cases}\implies t=t\implies \cfrac{30}{r+3}=\cfrac{18}{r-3}[/tex]
solve for "r"
