The magnetic field of Earth at a certain location is directed vertically downward and has a magnitude of $50.0 \mu \mathrm{T}$. A proton is moving horizontally toward the west in this field with a speed of $6.20 \times 10^{6} \mathrm{~m} / \mathrm{s}$. What are the direction and magnitude of the magnetic force the field exerts on the proton?