If wavelength of Balmer ${\mathrm{H}}_{\mathrm{\alpha }}$ line is XA^o. What will be the wavelength of ${\mathrm{H}}_{\mathrm{\beta }}$ line of Paschen series? 

$$\begin{gathered} \frac{1}{\mathrm{\lambda }}={\mathrm{R}}_{\mathrm{H}}\times {\mathrm{Z}}^2\left[\frac{1}{2^2}-\frac{1}{3^2}\right] \\ \frac{1}{\mathrm{x}}={\mathrm{R}}_{\mathrm{H}}\times {\mathrm{Z}}^2\left(\frac{5}{36}\right)\Rightarrow {\mathrm{R}}_{\mathrm{H}}\times {\mathrm{Z}}^2=\frac{36}{5\mathrm{x}} ; \frac{1}{\mathrm{\lambda }}={\mathrm{R}}_{\mathrm{H}}\times {\mathrm{Z}}^2\left[\frac{1}{3^2}-\frac{1}{5^2}\right]=\frac{16}{25\times 9}{\mathrm{R}}_{\mathrm{H}}{\mathrm{Z}}^2 \\ \frac{1}{\mathrm{\lambda }}=\frac{16}{25\times 9}\times \frac{36}{5\mathrm{x}}=\frac{64}{125\mathrm{x}} ; \mathrm{\lambda }=\frac{125\mathrm{x}}{64}{\mathrm{A}}^{\mathrm{o}} \end{gathered}$$