Light enters from air to glass plate having refractive index 1.5. The speed of light in glass is

a. 6.25 x 10⁷ms⁻¹
b. 5.5 x 10¹⁰ms⁻¹
c. 2 x 10⁸ms⁻¹
d. 4 x 10⁸ms⁻¹