A layer of oil 3 cm thick is floating on a layer of colored water 5 cm thick refractive index of colored water is $\large\frac{5}{3}$ and apparent depth of two liquids appears to be $\large\frac{36}{7}$cm. Then refractive index of oil:

Question

$(a)\;1.2 \\ (b)\;1.6 \\ (c)\;1.4 \\ (d)\;1.8 $