Two charged particles are fixed to an x-axis:

Two charged particles are fixed to an x-axis: Particle 1 of charge q1=2.1×10−8C is at position x = 20 cm and particle 2 of charge q2=−4.00q1 is at position x = 70 cm.
At what coordinate on the axis (other than at infinity) is the net electric field produced by the two particles equal to zero?