We know, refractive index (RI) of a medium = (speed of light in the air)/(speed of light in the medium)
According to the problem, 3/2 = (3 x 10^8 m/s)/(speed of light in glass)
Hence, speed of light in glass = (3 x 10^8 m/s)/(3/2) = 2 x 10^8 m/s .    (Ans.)