A plane electromagnetic wave of frequency 40 MHz travels in free space in the X-direction. At some point and at some instant, the electric field $\vec{E}$ has its maximum value of 750 N/C in Y-direction.

The magnitude and direction of magnetic field will be:

2.5 $\mu$T in Z-direction  

$ B_m = \frac{E_m}{c} = \frac{750}{3\times 10^8} = 2.50\times 10^{-6} T$

$\text{Magnetic Field is perpendicular to both electric field and direction of propogation i.e along Z- Axis}$