(a) In Lyman series $\left( \lambda_{\min} \right)_{L} = \frac{1}{R}$ and $\left( \lambda_{\min} \right)_{B} = \frac{4}{R}$
$\Rightarrow \left( \lambda_{\min} \right)_{B} = 4 \times \left( \lambda_{\min} \right)_{L} = 4 \times 912 = 3648\ \mathring{\mathrm{A}}$