electric field Questions

A particle of charge $-16\times 10^{-18}\text{C}$ moving with velocity $10\text{m/s}$ along the $x$ -axis enters a region where a magnetic field of induction $B$ is along the $y$ -axis, and an electric field of magnitude $10^4\text{V/m}$ is along the negative $z$ -axis. If the charged particle continues moving along the $x$ -axis, the magnitude of $B$ is: