Time period of a communication satellite \(=24\) hours.
Using kepler's third law,
\(T^2 \propto r^3\)
\(\Rightarrow \frac{T_c}{T_x}=\left(\frac{r_c}{r_x}\right)^{3 / 2}\)
\(\Rightarrow \frac{24}{T_x}=(4)^{3 / 2}\)
\(\Rightarrow T_x=\frac{24}{8}=3 \,hrs\)