Electromagnetics - finding wavelength from e_r and f

[a_lawson_2k]

Homework Statement

A transmission line is 1 meter and has a relative dielectric constant of 2.25
Find the phase velocity u and the wavelength λ for a frequency of 50 MHz.

Homework Equations

λ=?(ε_r, f)
u=λf

The Attempt at a Solution

I am unable to get from the relative dielectric constant and frequency to the wavelength. I could not find any such equation in my text.

My guess is the transmission line datum is extraneous, but I could be wrong.

 

[NascentOxygen]

I think this covers it. http://www.microwaves101.com/encyclopedias/560-light-phase-and-group-velocities

 

[rude man]

Thne length is immaterial, don't know why it's included.

To answer the question, what is the simple relationship between relative dielectric constant and the phase velocity? It applies to the transmission line and also to light. For light, think n for a hint.