A parallel plate capacitor is formed by two plates each of area $30\pi {\mathrm{cm}}^2$ separated by $1 \mathrm{mm}$. A material of dielectric strength $3.6\times {10}^7 \mathrm{V} {\mathrm{m}}^{-1}$ is filled between the plates. If the maximum charge that can be stored on the capacitor without causing any dielectric breakdown is $7\times {10}^{-6} \mathrm{C}$, the value of dielectric constant of the material is :

[Use $\frac{1}{4\pi {\epsilon }_o}=9\times {10}^9 \mathrm{N} {\mathrm{m}}^2 {\mathrm{C}}^{-2}$]