Question

An electron with kinetic energy K moving along the positive direction of an x axis enters a region in which a uniform electric field of magnitude E is in the negative direction of the y axis. A uniform magnetic field is to be set up to keep the electron moving along the x axis, and the direction of the field is to be chosen to minimize the required magnitude of the field. What is the magnitude of the magnetic field? (Use any variable or symbol stated above along with the following as necessary: me for the mass of an electron and e for the elementary charge.)