A capacitor of $10 \mu \mathrm{~F}$ capacitance whose plates are separated by 10 mm through air and each plate has area $4 \mathrm{~cm}^2$ is now filled equally with two dielectric media of $\mathrm{K}_1=2, \mathrm{~K}_2=3$ respectively as shown in figure. If new force between the plates is 8 N . The supply voltage is $\_\_\_\_$ V.