Answer
$0 \space \text{ miles}$
Work Step by Step
$ \begin{array}{l}
\mathrm{In\ this\ case,\ the\ river\ has\ an\ altitude\ of\ 7000} \ \mathrm{ft} .\ \mathrm{In\ other\ words} \ \mathrm{we\ need\ to}\\
\mathrm{apply\ the\ given\ formula\ and\ set} \ x\ =\ 7\ \mathrm{to\ find\ the\ distance\ of\ the\ Nile\ from\ }\\
\mathrm{the\ origin\ as\ follows} .\ \\\\
\begin{array}{ c c }
\dfrac{7-7}{0.639( 7) +1.75} =0\ (\mathrm{miles}) &
\end{array}
\end{array}$
