Speed of light changes according to the medium it is in.
in vacuum, speed of light is always  3x10^8 ms^ -1
formula required here is n= c/v 
where n is refractive index
c is speed of light in vacuum,
v is speed of light in medium.
substitute the values n find the answer.

This Is a Certified Answer

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
I hope you have given the data of refractive indexes correctly.  Normally water has 4/3 and  glass = 3/2.  You have given the other way round.

\mu_g=4/3,\ \ \ \mu_w=3/2\\\\c_{gl}=2*10^8m/s,\ \ \ c_w=?,\ c=?\\\\\mu_g=\frac{c}{c_{g}}\\\\In\ vacuum\ c=\mu_g*c_g=\frac{4}{3}*2*10^8=2.667*10^8 m/s\\\\c_w=\frac{c}{\mu_w}=\frac{2.667*10^8}{3/2}=1.778*10^8m/s

1 5 1