A Proton,with Mass 1

A proton,with mass 1.67 × 10^-27 kg and charge +1.6 × 10^-19 C,is sent with velocity 7.1 × 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.