The refractive index of glass is 1.5 . What is the speed of light in glass ? (speed of light in vacuum is $3 \times 10^{8}m/s$)

Question

$\begin{array}{1 1} 2 \times 10^8\;cm/s \\ 2 \times 10^8\;m/s \\ 2 \times 10^7\;cm/s \\ 2 \times 10^7\;m/s \end{array} $