An electron of mass $9.1 \times 10^{-31} \mathrm{kg}$ moves horizontally toward the north at $3.0 \times 10^{7} \mathrm{m} / \mathrm{s}$ . Determine the magnitude and direction of a $\vec{B}$ field that will exert a magnetic force that balances the gravitational force that Earth exerts on the electron.