Assuming that the flow of charge remains constant, we can just multiply 16microc by 4 because we want to know the amount of charge going by in four times the time.
16microc × 4 = 64microc
Now to find the amount of electrons, we know that one electron has a charge of 1.6x10^-19 C so we divide 64x10^-6 C by that.
64x10^-6 / 1.6x10^-19 = 4x10^14 electrons
