Solution (source code)

= Solution

The divergence equation requires $B_3=0$, and the wave equation requires
$$
\boxed{\omega^2=c^2k^2}.
$$
For propagation in the positive $z$ direction, Faraday's law gives
$$
\boxed{
\mathbf E=\frac\omega k(B_2,-B_1,0)\cos(kz-\omega t)}.
$$
\b[Thus $\mathbf E$, $\mathbf B$, and the propagation direction are mutually perpendicular.]