A parallel plate capacitor is of area  $6c{m}^2$ and a separation $3mm$. The gap is filled with three dielectric materials of equal thickness (see figure) with dielectric constants ${\text{K}}_1=10$,  ${\text{K}}_2=12$ and ${\text{K}}_3=14$. The dielectric constant of a material which give same capacitance when fully inserted in above capacitor, would be