electromagnetic wave, the electric field vector $\vec{E}$ and magnetic field vector $\vec{B}$ show their variations perpendicular to the direction of propagation of wave as well as perpendicular to each other. As the electromagnetic wave is travelling along z-direction, hence $\vec{E}$ and $\vec{B}$ show their variation in x-y plane. Wavelength, λ = $\frac{c}{v}$ = $\frac{3\times10^{8}\text{m/s}}{30\times10^{6}\text{s}^{-1}}$ = 10 m