Three charges are located in the $x-y$ plane (see plot below), with $Q_1 = -6.00 μC$, $Q_2 = 2.00 μC$ and $Q_3 = 3.00 μC$. Note that the charges are located at grid intersections points.
Calculate the work required (by external forces) to transport $Q_3$ from its location on the figure to infinity.
Hint: Use the conservation of energy. Compute the potential energy of the system at the start and the end. The difference is the work required.