Why can't radio 4 FM reach listeners in deep valleys?

[manjula]

Homework Statement

Radio 4 transmits on FM at a frequency of 92.5 MHz Calculate the wavelength and use it to explain why listeners in deep valleys cannot pick up radio 4 FM.

Homework Equations

The Attempt at a Solution

 

[LowlyPion]

First of all what is the wavelength.

If you don't know that you might really not know where to start.