Finding wavelength from refractive index and plasma frequency

[virgileso]

I'm trying to determine the wavelength of a particular situation. I'm given the refractive index of the metal and the value of the plasma frequency, and I'm asked to find the wavelength (or frequency) of a particular ray in this situation. Unfortunately, I'm not terribly able to even begin answering this question. Help?

 

[Dale]

Wavelength times frequency gives you the wave propagation velocity. You have frequency, is there any way to determine the wave propagation velocity from the given information?