For first member of Paschen series \(n = 4\)
\(\frac{1}{{{\lambda _1}}} = R\,\left[ {\frac{1}{{{3^2}}} - \frac{1}{{{4^2}}}} \right] \Rightarrow \frac{1}{{{\lambda _1}}} = \frac{{7R}}{{144}}\)
\( \Rightarrow R = \frac{{144}}{{7{\lambda _1}}} = \frac{{144}}{{7 \times 18800 \times {{10}^{ - 10}}}} = 1.1 \times {10^{ - 7}}\)
For shortest wave length \(n = \infty \)
So \(So\frac{1}{{{\lambda _{}}}} = R\,\left[ {\frac{1}{{{3^2}}} - \frac{1}{{{\infty ^2}}}} \right] \Rightarrow \frac{R}{9}\)
\( \Rightarrow \lambda = \frac{9}{R} = \frac{9}{{1.1 \times {{10}^{ - 7}}}} = 8.225 \times {10^{ - 7}}m = 8225\,{ Å}\)