A parallel plate capacitor is formed by two plates each of area $30 \pi \mathrm{~cm}^2$ separated by 1 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 :
$\left\{\right.$ Use : $\left.\frac{1}{4 \pi \varepsilon_0}=9 \times 10^9 \mathrm{Nm}^2 \mathrm{C}^{-2}\right\}$