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 E has its maximum value of 750 N/C in Y-direction, the magnitude and direction of magnetic field will be:

2.5 µT Z-direction

$B_m=\frac{E_m}{C} = \frac{750}{3 \times 10^8}$ = 2.5 µT Z-direction