A particle of charge $–16\times {10}^{–18}$ coulomb moving with velocity  $10 m{s}^{–1}$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 ${10}^4 V/m$ is along the negative $z$-axis. If the charged particle continues moving along the$x$-axis, the magnitude of $B$ is