Particle 1 carrying \(-4.0 \mu \mathrm{C}\) of charge is fixed at the origin of an \(x y\) coordinate system, particle 2 carrying \(+6.0 \mu \mathrm{C}\) of charge is located on the \(x\) axis at \(x=3.0 \mathrm{~m}\), and particle 3 , identical to particle 2 , is located on the \(x\) axis at \(x=-3.0 \mathrm{~m}\). What is the vector sum of the electric forces exerted on particle 3?