Assignment:
Using the physical conditions present in the universe during the era of recombination (T=3000 and pm=10^-18 kg/m^3), show by calculation that the Jeans length for the universe at that time was about 100 ly and that the total mass contained in a sphere with this diameter was about 4x10^5 Msun.
Provide complete and step by step solution for the question, use formulas.