Problem: Two spherical objects are separated by a distance of 1.44 x 10-3 m. The objects are initially electrically neutral and are very small compared to the distance between them. Each object acquires the same negative charge due to the addition of electrons. As a result, each object experiences an electrostatic force that has a magnitude of 2.18 x 10-20 N.
Part A: How many electrons did it take to produce the charge on one of the objects?
Please explain clearly with details so that I can follow.