One electron has a charge of 1.602 x 10^-19 Coulombs (C), so to calculate the total number of electrons, we divide the total charge 4.0 x 10^-9 C by the charge of a single electron. This gives us:
4.0 x 10^-9 / 1.602 x 10^-19 = 2.5 x 10^10 electrons that are removed from the penny