Question

In a cathode ray tube, a beam of electrons is injected horizontally into the exact center of the parallel-plate region. Here L = 3.0 cm and d = 0.20 cm. The top plate has a surface charge density of σ0 = +0.15 μC / m2, and the bottom plate has a surface charge density of −σ0. The electrons are injected with a speed of v = 5 × 107 m/s. After a single electron traverses a horizontal distance L, through what change in electric potential (in Volts) does it move?

I am completely lost here. Please help!