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 $3.6\times {10}^7{\mathrm{Vm}}^{-1}$ 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 :

$\left\{\text{ Use }:\frac{1}{4\pi {\epsilon }_0}=9\times {10}^9{\mathrm{Nm}}^2{\mathrm{C}}^{-2}\right\}$