(b) $\frac{\lambda}{\lambda_{0}} = \frac{\left\lbrack \frac{1}{2^{2}} - \frac{1}{3^{2}} \right\rbrack}{\left\lbrack \frac{1}{2^{2}} - \frac{1}{4^{2}} \right\rbrack} = \frac{5}{36} \times \frac{16}{3} = \frac{20}{27}$
$\lambda = \frac{20}{27}\lambda_{0}$