The refractive index of glass is 1.5 what is the speed of light in vaccum is $3.0 \times 10^8 \;ms^{-1}$

Question

$\begin{array}{1 1} 2 \times 10^8\;ms^{-1} \\ 2 \times 10^8 \;cm^{-1} \\ 2 \times 10^{7}\;ms^{-1} \\ 2 \times 10^{7} cm^{-1} \end{array}$