The problem states that a piece of stone "weighs 15kg". In physics, "weight" is a force, but when given in kilograms, it refers to the mass of the object. The volume is given as 40 m3.

The problem states that a piece of stone "weighs 15kg". In physics, "weight" is a force, but when given in kilograms, it refers to the mass of the object. The volume is given as $40 \text{ m}^3$.
Mass ($m$) = $15 \text{ kg}$
Volume ($V$) = $40 \text{ m}^3$

Density ($\rho$) is defined as mass per unit volume.

The calculated density is $0.375 \text{ kg/m}^3$, which matches option A.

The final answer is $\text{A. } 0.375 \text{ kg/m}^3$.