How would i solve this?

23.2.2 Velocity Selector 1) Velocity selector: A proton, with mass 1.67 x 10-27 kg and charge +1.6 x 10-19 C, is sent with velocity 7.1 x 104 m/s in the +x direction into a region where there is a uniform electric field of magnitude 730 V/m in the +y direction. What are the magnitude and direction of the uniform magnetic field in the region, if the proton is to pass through undeflected? Assume that the magnetic field has no x-component and neglect gravitational effects