Estimate what neutrino rest mass (in eV) would provide the critical density to close the universe. Assume

Question:

Estimate what neutrino rest mass (in eV) would provide the critical density to close the universe. Assume the neutrino density is, like photons, about 109 times that of nucleons, and that nucleons make up only.
(a) 2% of the mass needed, or
(b) 5% of the mass needed.