A tub is filled with water and a wooden cube $10 \mathrm{~cm} \times 10 \mathrm{~cm} \times 10 \mathrm{~cm}$ is placed in the water. The wooden cube is found to float on the water with a part of it submerged in water. When a metal coin is placed on the wooden cube, the submerged part is increased by 3.87 cm . The mass of the metal coin is $\_\_\_\_$ gram. (Take water density as $1 \mathrm{~g} / \mathrm{cm}^3$ and density of wood as $0.4 \mathrm{~g} / \mathrm{cm}^3$ )