I believe that the correct given values are:
density = 755 kg/m^3
volume = 640 cm^3
First let us convert volume to m^3 units.
volume = 640 cm^3 * (1 m / 100 cm)^3 = 6.4 x 10^-4 m^3
so the mass is:
mass = 755 kg/m^3 * (6.4 x 10^-4 m^3)
mass = 0.4832 kg = 483.2 g
