A large metal plate has a surface charge density of $8.85\times {10}^{-6} \mathrm{C} {\mathrm{m}}^{-2}$. An electron having initial kinetic energy of $8\times {10}^{-17} \mathrm{J}$ is moving towards the center of the plate. If the electron stops just before reaching the plate then the initial distance between the electron and the plate is [Take ${\epsilon }_0=8.85\times {10}^{-12} {\mathrm{C}}^2 \mathrm{N} {\mathrm{m}}^{-2}$]