Electrostatic Potential and Capacitance Part 1

A parallel plate capacitor is of area 6 cm2 and a separation 3 mm. The gap is filled with three dielectric materials of equal thickness (see figure) with dielectric constants K1, = 10, K2 = 12 and K3 = 14. The dielectric constant of a material which whenfully inserted in above capacitor, gives same capacitance would be :