A plane electromagnetic wave of frequency $25\: MHz$ travels in free space along the $x$ - direction. At a particular point in space and time, $E= 6.3 \: jV/m$. What is B at this point?

Question

$\begin {array} {1 1} (a)\;2.1 \times 10^{-6}i\: T & \quad (b)\;0.21 \times 10^{-8}i\: T \\ (c)\;2.1 \times 10^{-8}k\: T & \quad (d)\;0.21 \times 10^{-8}j\: T \end {array}$