A plane electromagnetic wave with a frequency of $30 \mathrm{MHz}$ travels in free space. At a particular point in space and time, the electric field is $6 \mathrm{V} {\mathrm{m}}^{-1}$. The magnetic field at this point will be $x\times {10}^{-8} \mathrm{T}$. The value of $x$ is,