Suppose that the electric field part of an electromagnetic wave in vaccum is $E= 3.1 \times N/c $ cos $[(1/8 rad/m)y +(5.4 \times 10^8\;rad/s/t)$ what is the amplitude of the magnetic field part of the wave ?

Question

$\begin{array}{1 1} 3\;m \\ 3.2 \;m \\ 3.4 \;m \\ 3.5\;m \end{array} $