Hello there,
To answer your first question, we can use the equation for the kinetic energy of an electron, which is KE = ½ mv^2, where m is the mass of the electron and v is its final velocity. We know that the potential difference (V) is equal to the change in electric potential energy (ΔPE) divided by the charge (q), so we can rewrite the equation as KE = qV. Plugging in the values, we get KE = (1.6 x 10^-19 C)(400 V) = 6.4 x 10^-17 J. Therefore, the final kinetic energy of the electron would be 6.4 x 10^-17 joules.
For your second question, we can use the equation for the work done by an electric force, which is W = ΔPE = qΔV, where ΔV is the change in potential difference and q is the charge. Since we are bringing four point charges, we can simply multiply the equation by 4 to get the total work required. Plugging in the values, we get W = 4(-8 x 10^-6 C)(3 x 10^-9 m) = -9.6 x 10^-14 J. Therefore, the work required to bring the four charges to a distance of 3 nm from each other would be 9.6 x 10^-14 joules.
I hope this helps! Let me know if you have any further questions.