Wavelength/Frequency inside a cavity

[Capt. Pantsless]

http://www.cengage.com/resource_uploads/static_resources/0534493394/4891/Ch03-WebAppendix01.pdf

I've been doing some reading and I came across a mathematical step that is confusing me.
Could someone explain to me how they get from equation 3.45 to equation 3.46 in the link that I have posted above?

It looks to me as though (f²/c³) has somehow become λ^-4.

 

[Capt. Pantsless]

Ah, I just figured it out! The answer lies in the earlier part of the derivation. D'oh!