Find the wave length of EM wave of frequency $6 \times 10^{12}\;Hz$ in free space .

Question

$\begin{array}{1 1} 5 \times 10^{-5}m\;u.v \;rays \\ 5 \times 10^{-6}\;m\;,u.v\; rays \\ 5 \times 10^{-5}m\;I.R\;rays \\ 5 \times 10^{6}\;u.v\; rays \end{array}$