Show that the fermi energy for nonrelativistic electrons (treated as if they do not interact with each other) confined in the two-dimensional square box is given by h2n ef= l2 where n is the number of electrons, l is the length of the side of the square, and m is the mass of an electron such confinement to a plane happens, for example, for electrons in the layered materials that are used to make high-temperature superconductors