$\textbf{Three-Dimensional Anisotropic Harmonic Oscillator}$. An oscillator has the potential-energy function $U(x, y, z) = {1\over2} k{'_1}(x^2 + y^2) + {1\over 2} k{'_2}z^2$, where $k{'_1} > k{'_2}$. This oscillator is called $anisotropic$ because the force constant is not the same in all three coordinate directions. (a) Find a general expression for the energy levels of the oscillator (see Problem 41.44). (b) From your results in part (a), what are the ground-level and first-excited-level energies of this oscillator? (c) How many states (different sets of quantum numbers $nx, ny,$ and $nz$) are there for the ground level and for the first excited level? Compare to part (c) of Problem 41.44.