when multiple layers of liquid of height $h_1$ and $h_2$ of refractive index $\mu_1$ and $\mu_2$ respectively are present in tank and an object at the bottom is viewed from top . then ,

apparent depth $= \large\frac{h_1}{\mu _1} +\frac{h_2}{\mu_2}$

$\therefore $ apparent depth $=\large\frac{20}{1.33} +\frac{40}{1.46}$

$\qquad= 42 \;cm$

Hence d is the correct answer