If an electron moves from rest from a point at which potential is 50 volt to another point at which potential is 70 volt, then its kinetic energy in the final state will be .....
$ K.E = q_o (V_A - V_B ) = 1.6 \times 10^{-6} (70- 50) = 3.2 \times 10^{-18 } J $