Two hydrogen atoms collide head on and end up with zero kinetic energy.Each atom then emits a photon of wavelength 121.6nm.Which transition leads to this wavelength ?How fast were the hydrogen atoms traveling before collision?$R_H=1.097\times 10^7m^{-1}$ and $m_H=1.67\times 10^{-27}Kg$

Question

$\begin{array}{1 1}(a)\;4.43\times 10^4m/s&(b)\;2.43\times 10^4m/s\\(c)\;4.43\times 10^2m/s&(d)\;1.6\times 10^4m/s\end{array}$