Does anyone know how to derive the following formula?

Nb/Ny=(Omega-b*Ey)/(Omega-y*Eb)

Whe
Omega-b is Omega Baryon
Ey is the energy of a CMB photon = 2.7kT, where T=2.725
Omega-y is the ratio of CMB radiation density to the critical density
Eb=Mb*c^2, where Mb is the mass of a baryon


[[Mod. note -- This at least appears like it might be a university
homework problem. If so, people posting followups should keep in mind
that (much) more information is generally imparted by general suggestions
to help the student learn for herself, than by simply providing a
solution. -- jt]]