When a test charge q0 = 3 nC is placed at the origin, it experiences a force of 8*10-4 N in the positive y direction.
(a) What is the electric field at the origin?
(b) What would be the force on a charge of -4 nC placed at the origin?
(c) If this force is due to a charge on the y axis at y = 3 cm, what is that charge (magnitude and sign)?