Actually, ng = 3/2 and nw = 4/3.
Absolute Refractive Index of a medium = Speed of light in vacuum/Speed of light in the medium
Speed of light in glass = 2 x 10^8 m/s
Speed of Light in Vacuum = (3/2) x 2 x 10^8 m/s = 3 x 10^8 m/s
Speed of light in water = (3 x 10^8 m/s)/(4/3)
= 2.25 x 10^8 m/s