Answer
$425\;km$.
Work Step by Step
The distance on the map measures $a=5\;cm$.
Let the actual distance is $=d$.
Equate the scare drawing ratio with $a:d$.
$\Rightarrow \frac{1}{85}=\frac{5}{d}$
Cross multiply.
$\Rightarrow 1d=85(5)$
Simplify.
$\Rightarrow d=425\;km$.
