The lowest transition in Balmer series is from $\mathrm{n}_1=2$ and $\mathrm{n}_2=3$
$\therefore \quad \overline{\mathrm{v}}=\mathrm{R}_{\mathrm{H}}\left[\frac{1}{\mathrm{n}_1{ }^2}-\frac{1}{\mathrm{n}_2^2}\right]=\mathrm{R}_{\mathrm{H}}\left[\frac{1}{2^2}-\frac{1}{3^2}\right]=\mathrm{R}_{\mathrm{H}}\left[\frac{5}{36}\right]$