A system consisting of two charges \(7\ \mu C\) and \(-2\ \mu C\) (and with no external field) placed \((0,0)\) respectively at \(\left(-9\;\text{cm},0,0\right)\) and \((9\;cm, 0,0)\) respectively. Suppose that the same system of charges is now placed in an external electric field \(E=A\left(1\text /r^2\right),\ A=9\times 10^5\ C\ m^{-2}\). What would the electrostatic energy of the configuration be?