The difference energy between two energy levels is
ΔE=2.18×10−18[n121−n221]J
1.47×10−17=2.18×10−18×(9)((n)21−(n+1)21)
0.749=n21−(n+1)21
n=1
Hence, the transition is taking place between 1→2, and it comes under Lymann series.
If we take 0.749≃0.75=43