A parallel-plate capacitor has the space between the plates filled with two slabs of dielectric, one with

Question:

A parallel-plate capacitor has the space between the plates filled with two slabs of dielectric, one with constant K1 and one with constant K2 (Fig). The thickness of each slab is the same as the plate separation d, and each slab fills half of the volume between the plates. Show that the capacitance is