Answer
See the answer below.
Work Step by Step
The lowest energy line is in the transition from n=6 to n=5.
$\Delta E=-Rhc(1/n_f^2-1/n_i^2)$
$\Delta E=-2.66\times10^{-20}\ J$
For a photon with this energy:
$E=h\times\nu$
$\nu=4.02\times10^{13}\ 1/s$
$c=\lambda\times\nu$
$\lambda=7.46\times10^{-6}\ m$
