Plate is oscillating

A parallel plate capacitor is completely filled with a dielectric sheet of thickness $d$ and relative permittivity $k$ is placed on a horizontal tabletop. The lower plate is glued to the tabletop and the dielectric slab is glued to the lower plate. The plates are square of edge length $l$ and mass of the upper plate is $m$ . The plates are given a charge $+q$ and $-q$ , then the upper plate is shifted horizontally by a small distance $x$ along one of its edges and set free. Find the period of oscillation of this plate. Thickness d of the dielectric is much smaller than the edge length $l$ .

Details: $\epsilon_0 m k = 10^{-6}$ , $l=100 \text{ m}$ , $x=1 \text{ cm}$ , $d=1 \text{ m}$ and $q=0.1 \text{ C}$ .