The refractive index of water with respect to vacuum is 4/3 and refractive index of vacuum with respect to glass is 2/3. if the speed of light in glass is 2x 108m/s, find the speed of light in i) vacuum ii) water

As we know that

now for the first part we know that

refractive index of vacuum with respect to glass is 2/3

speed of light in glass is

now we will have

Part b)

Now similarly we can say

here refractive index of water with respect to vacuum is 4/3

now we will have

your answer is c! hope this : )