Given : Frequency of wave $f=5\mathrm{GHz}$

$=5\times {10}^9 \mathrm{Hz}$

Relative permittivity, ${ϵ}_r=2$ and Relative permeability, ${\mu }_{\mathrm{r}}=2$ Since speed of light in a medium is given by,

$v=\frac{{\displaystyle 1}}{{\displaystyle \sqrt{\mu }\in }}=\frac{{\displaystyle 1}}{{\displaystyle \sqrt{{\mu }_r{\mu }_0·{ϵ}_r{\in }_0}}}$

$v=\frac{1}{\sqrt{{\mu }_r{ϵ}_f}}\frac{1}{\sqrt{{\mu }_0{ϵ}_0}}=\frac{C}{\sqrt{{\mu }_r{ϵ}_r}}$

Where $C$ is speed of light is vacuum

$\therefore v=\frac{{\displaystyle 3\times {10}^8}}{{\displaystyle \sqrt{4}}}=\frac{{\displaystyle 30\times {10}^7}}{{\displaystyle 2}} \mathrm{m} {\mathrm{s}}^{-1}$

$=15\times {10}^7 \mathrm{m} {\mathrm{s}}^{-1}$

$\therefore$ Ans. is $15$