First condition \(\frac{1}{\lambda } = R\,\left[ {\frac{1}{{{1^2}}} - \frac{1}{{{2^2}}}} \right] \Rightarrow R = \frac{4}{{3\lambda }}\)
Second condition \(\frac{1}{{\lambda '}} = R\,\left[ {\frac{1}{{{1^2}}} - \frac{1}{{{3^2}}}} \right]\)
\( \Rightarrow \lambda ' = \frac{9}{{8R}} \Rightarrow \lambda ' = \frac{9}{{8 \times \frac{4}{{3\lambda }}}} = \frac{{27\lambda }}{{32}}\)