(a) For Balmer series $\frac{1}{\lambda} = R\left( \frac{1}{2^{2}} - \frac{1}{n^{2}} \right)$ where $n = 3,\ 4,\ 5$
For second line $n = 4$
So $\frac{1}{\lambda} = R\left( \frac{1}{2^{2}} - \frac{1}{4^{2}} \right) = \frac{3}{16}R \Rightarrow \lambda = \frac{16}{3R}$