A plane electromagnetic wave of frequency $40 \mathrm{MHz}$ travels in free space in the $x$-direction. At some point and at some instant, the electric field $\overrightarrow{E}$ has its maximum value of $750 \mathrm{N} {\mathrm{C}}^{-1}$ in the $y$-direction. The magnitude and direction of the magnetic field will be -