Question

In the figure, an electron acc. from rest through potential difference V1=1.00kV enters the gap between two parallel plates having separtion d=20.00mm and potential difference V2=100v. The lower plate is at the lower potential. Neglect fringing and assume the electron's velocity vector is perpendicular to the electric field vector between the plates. In unit vector notation, what uniform magnetic field allows the electron to travel in a straight line in the gap?