Calculate the wave number of lines having the frequency of $5 \times 10^{16}$ cycles per sec

Question

$\begin{array}{1 1} (a)\;1.666 \times 10^8\;m^{-1} \\(b)\;2.666 \times 10^8\;m^{-1}\\ (c)\;0.666 \times 10^8\;m^{-1}\\ (d)\;3.666 \times 10^8\;m^{-1}\end{array}$