A 3 cm thick iron open box is made whose external dimensions are 78 cm x 54 cm x 12 cm. Find the weight of the box if its density is 60 gm/cm³.

Thickness of the iron sheet = 3 cm
External dimensions at the box = 78 cm x 54 cm x 12 cm
Therefore internal dimensions of the box = 72 m x 48 cm x 9 cm
Volume of the iron used in making the box 
          = External volume of the box - Internal volume 
          = 78 x 54 x 12 - 72 x 48 x 9
          = 50544 - 31104 = 19440 cm³
Weight = Volume x density
         = 19440 x 60 gm
         = 1166.4 kg