Two point charges, $Q_1 = +4 \mu C$ and $Q_2 = -9 \mu C$, are placed at positions $(0,0)$ and $(5,0)$ meters respectively on the x-axis. A third point charge $Q_3 = +2 \mu C$ is to be placed on the x-axis such that the net electrostatic force on it is zero.
Determine the x-coordinate of the position where $Q_3$ should be placed for equilibrium.