To find mass of the cube first find volume of cube material
edge of cube = 10 cm
edge of inner cube (hollow space) = 10 - (2.5+2.5) = 5 cm
total volume of cube = 10^3 = 1000
total volume empty space = 5^3 = 125
Volume of cube material = 1000 - 125 = 875 cm^3
Mass of cube = density x volume = 7.9x10 x 875 = 69125 g = 69.125 kg
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