P = m/v
To find the mass you have to do Density x Volume.
The volume of the cuboid is 0.18 m cubed and the density is 2.7g/cm cubed.
The 2.7 g/cm cubed must be converted into kg/m cubed to find the mass in kg. Which is 2,700 kg/ m cubed.
2,700 x 0.18 = 486 kg.
The mass of the marble in kg is 486kg