For a quantum well $(QW)$ as shown here, the width is W and the effective mass of the electron in this well is $m_{\text{e}\text{f}\text{f}\text{.}}$ From the quantum physics, we found there are four available levels in the QW $($two for conduction and two for valence$).($a$)(3$pts$)$ What if W is reduced, what will happen to these quantum levels? $($b$)(7$pts$)$ Now, we only look at the conduction band of the QW $.$ If there is a quasi$-$Fermi level between $n=1$ and $n=2$ conduction sub$-$bands, what will the electron concentration at the first conduction subband