Problem in Deriving Rayleigh-Jeans Formula

[MnFeCo]

Hi I am having trouble with the derivation of the Rayleigh-Jeans from the steps shown at the hyperphysics web site. I have emailed Dr. Rod Nave who is listed as the person-in-charge at the site but I have been able to get a reply. It would really be much appreciated if anyone can have a look at the uploaded file here and follow the queries I make on the PDF (which is the same thing I sent to the hyperphysics administrator).

Thank You.

 

[MnFeCo]

Sorry I made a typo, I meant that I have been unable to receive a reply to date to the email I sent to hyperphysics.