A 4-level system at 1000K which is having the N particles with energy levels (ε1 - ε0) = 0.15eV, (ε2-ε0) = 0.45eV, and (ε3-ε0) = 0.75eV. Each level has a degeneracy = 1. And the system contains Avogadro's number of particles. Determine the system energy at the 1000K in J/mol.