Just an update. I asked one of the people who wrote the Pset about this question and he said that the other solutions are formed from linear combinations of degenerate states of the harmonic oscillator eigenfunctions. Another solution would be Ψ=ψ2,0,0(x,y,z)+ψ0,2,0(x,y,z)+ψ0,0,2 (x,y,z) since...