v=λf . This equation is supposed to calculate the speed of a wave(such as light) in a medium, such as glass. But the numbers you have gives the speed of the wave as 20 times greater than the speed of light in a vacuum, which is NOT POSSIBLE!!. λ cannot be: 3 x 10^8, which is the speed of light in a vacuum. You must modify your numbers. v must come out as LESS than speed of light in a vacuum. Check carefully to see where you went wrong.
