A particle of mass 10 g and charge 80C moves through a uniform magnetic field, in a

Question:

A particle of mass 10 g and charge 80μC moves through a uniform magnetic field, in a region where the free-fall acceleration is -9.8j m/s2. The velocity of the particle is a constant 20i km/s, which is perpendicular to the magnetic field. What, then, is the magnetic field?