a
(a) Probable frequencies of tuning fork be $n + 4$ or $n - 4$
Frequency of sonometer wire $n \propto \frac{1}{l}$.
$\therefore $ $\frac{{n + 4}}{{n - 4}} = \frac{{100}}{{95}}$ or $95\,(n + 4) = 100(n - 4)$
or $95n + 380 = 100n - 400$ or $5n = 780$ or $n = 156$