Two point charges 100μC and 5μC are placed at points A and B respectively with AB = 40cm. The work done by external force in displacing the charge 5μC from B to C, where BC = 30cm, angle $\mathrm{ABC}=\frac{\mathrm{\pi }}{2}\mathrm{and} \frac{1}{4{\mathrm{\pi \epsilon }}_0}=9\times {10}^9{\mathrm{Nm}}^2/{\mathrm{C}}^2$