$${y = \frac{QE}{2mv_x^2} \\ = \frac{(1,5 \times 10^{-13}\, \mathrm{C})(1,4 \times 10^6\, \mathrm{N/C})(1,5 \times 10^{-2}\, \mathrm{m})^2}{(2)(1,3 \times 10^{-10}\, \mathrm{kg})(18\, \mathrm{m/s})^2} \\ = 6,4 \times 10^{-4}\, \mathrm{m} \\ = \underline{\underline{0,64\, \mathrm{mm}}}}$$