$${d = \frac{(2e)(79e)}{4 \pi \varepsilon_0 K_{\alpha}} \\ = \frac{(2 \times 79)/1,60 \times 10^{-19}\, \mathrm{C})^2}{4 \pi \varepsilon_0 (5,30\, \mathrm{MeV})(1,60 \times 10^{-13}\, \mathrm{J/MeV})} \\ = \underline{\underline{4,29 \times 10^{-14}\, \mathrm{m}}}}$$