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

Question

$\begin{array}{1 1} 8.6\;MHZ \\ 86\;MHZ \\ 0.86\;MHZ \\ 860\;MHZ \end{array} $