A mineral oil has a density of 0.875 g/cm3. Suppose you spread 0.60 g of this oil over the surface of water in a large dish with an inner diameter of 21.6 cm. How thick is the oil layer

With a density of 0.875 g/cm³, a sample of 0.60 g of this oil would have a volume V such that

0.875 g/cm³ = (0.60 g)/V   ==>   V ≈ 0.686 cm³

If the oil is spread out uniformly over the water's surface, then it forms a cylinder whose diameter is equal to that of the dish, 21.6 cm. Then the thickness d of the oil cylinder is such that

V = π ((21.6 cm)/2)² d   ==>   d ≈ 0.0202 cm