In a vacuum, the electromagnetic wave travels in the z-direction. In the $x-y$ plane, there is an electric field (E) and a magnetic field $(\mathrm{H})$. They are perpendicular to one other.

Frequency of the wave, $v$ is given as $30 \mathrm{MHz}=30 \times 10^{6} \mathrm{~s}^{-1}$

Speed of light in vacuum is known as $C=3 \times 10^{8} \mathrm{~m} / \mathrm{s}$

Wavelength of a wave can be calculated by the expression:

$\lambda=\frac{c}{v}$

$=\frac{3 \times 10^{8}}{30 \times 10^{\circ}}=10 \mathrm{~m}$