Answer
$4.7\times10^{-3}\,Hz$
Work Step by Step
Given/Known: $c= 3.0\times10^{8}\,m/s$,
Radius of earth $R_{E}=6.4\times10^{6}\,m$
Wavelength $\lambda=1.0\times10^{4}\times R_{E}= 1.0\times10^{4}\times6.4\times10^{6}\,m$
Recall: Frequency $\nu =\frac{c}{\lambda}$
Result: $\nu=\frac{3.0\times10^{8}\,m/s}{1.0\times10^{4}\times6.4\times10^{6}\,m}=4.7\times10^{-3}\,Hz$
