Apparent depth $=\large\frac{t_1}{\mu_1}+\frac{t_2}{\mu_2}$

$\therefore \large\frac{36}{7}=\frac{5}{\Large\frac{5}{3}}+\frac{3}{\mu_2}$

$\large \frac{3}{\mu_2}=\frac{36}{7}$$-3 =\large \frac{15}{7}$

$\therefore \mu_2=\large\frac{7}{5}$$=1.4$

Hence c is the correct answer.