\(\frac{1}{{{\lambda _0}}} = R\left[ {\frac{1}{{{2^2}}} - \frac{1}{{{3^2}}}} \right] = R\left[ {\frac{1}{4} - \frac{1}{9}} \right] = \frac{5}{{36}}R\,…..(i)\)
\(\frac{1}{{\lambda '}} = R\left[ {\frac{1}{{{2^2}}} - \frac{1}{{{4^2}}}} \right] = R\left[ {\frac{1}{4} - \frac{1}{{16}}} \right] = \frac{{3R}}{{16}}\,…..(ii)\)
\(\frac{{\lambda '}}{\lambda } = \frac{{5R}}{{36}} \times \frac{{16}}{{3R}} = \frac{{20}}{{27}}\)
\(\Rightarrow\) \(\lambda ' = \frac{{20}}{{27}}{\lambda _0}\)