$ F = \frac{ 1}{4\pi \epsilon _{0} } \cdot \frac{Q_{1} \cdot Q_{2} }{ r^{2} } $

$ r = \sqrt{\frac{ 1}{4\pi \epsilon _{0} } \cdot \frac{Q_{1} \cdot Q_{2} }{ F}} $

$ Q_{1} = 4\pi \epsilon _{0} \cdot \frac{F\cdot r^{2} }{ Q_{2} } $