A plane electromagnetic wave of frequency $30 \mathrm{MHz}$ is travelling along $\hat{\mathrm{k}}$ - direction. At a particular point of space and time of propagation, if the electric field is given by $\overrightarrow{E}=30 \mathrm{Volts} {\mathrm{meter}}^{-1}$ $\left(-\hat{\mathrm{i}}\right),$ then the corresponding magnetic field is