$\begin{aligned} & \text { Refractive index of medium } \\ & \qquad=\frac{\text { speed of light in vacuum }}{\text { speed in medium }} \\ & \Rightarrow \text { Speed of light in medium } \\ & =\frac{\text { speed of light in vacuum }}{\text { refractive index }} \\ & \Rightarrow \quad v=\frac{\mathrm{c}}{\mathrm{n}}=\frac{3 \times 8^8}{1.4}=2.14 \times 10^8 \mathrm{~m} / \mathrm{s}\end{aligned}$