A constant voltage of V is applied to a partially filled parallel plate capacitor. The relative permittivity of the material is 2, the area of the capacitor is S=1mm2 , and the spacing between the plates is d=3mm. What should the thickness of the dielectric slab, x, be so that the energy stored in the dielectric is equal to the energy stored in the free space region of the capacitor. You can ignore the fringing fields. Report your answer in mm