Solving Mathematics in Plato's Writings: La leçon de Platon

[Kobzar]

Hello, everybody:
I am translating La leçon de Platon, by Dom Néroman (La Bégude de Mazenc, Arma Artis, 2002), which deals with music theory and mathematics in the works of Plato. The problem which brings me here is not about translation, but about mathematics, although a proper understanding of these is necessary for a proper translation. Please see attached document.
Thank you very much in advance!
All best!

 

[MountEvariste]

Your answer and workings are correct.

See here.

 

[Kobzar]

Your answer and workings are correct.

See here.

Thank you very much!