The index of refraction of a certain glass is measured to be 1.5. what is the speed of light in that glass? (c = 3.0 × 108 m/s)

You throw a small rock straight up from the edge of a highway bridge that crosses a river. the rock passes you on its way down, 7.00 s after it was thrown. what is the speed of the rock just before it reaches the water 28.0 m below the point where the rock left your hand? ignore air resistance.