Answer
$0.13Km$
Work Step by Step
We know that
$r_{\circ}=r_1 10^{\frac{\beta}{20}}$
We plug in the known values to obtain:
$r_{\circ}=(18cm)(\frac{10^{-2}m}{1cm})10^{\frac{57}{20}}$
$r_{\circ}=0.13\times 10^3m(\frac{1Km}{10^3m})$
$r_{\circ}=0.13Km$
