We know that density = mass / volume
Volume of a cube = a^3
Where a= length of a side
Given :
edge length of cube = 2.50 cm
so volume of cube of copper = 2.50 X 2.50 X 2.50 = 15.625 cm^3
mass of copper = 140.125 g
So density = Mass / Volume = 140.125 / 15.625 = 8.968 g / cm^3