A point charge $q_{1}=+5.0 \mu \mathrm{C}$ is fixed in place at $x=0$ and a point charge $q_{2}=-3.0 \mu \mathrm{C}$ is fixed at $x=-20.0 \mathrm{cm}$ Where can we place a point charge $q_{3}=-8.0 \mu \mathrm{C}$ so that the net electric force on $q_{1}$ due to $q_{2}$ and $q_{3}$ is zero?