19. A metal sheet 27 cm long, 8 cm broad and 1 cm thick is melted into a cube. The difference between the surface areas of two solids, is :

20. A tank 3 m long, 2 m wide and 1.5 m deep is dug in a field 22 m long and 14 m wide. If the earth dug out is evenly spread out over the field, the rise in level of the field will be :

21. The sum of length, breadth and depth of a cuboid is 19 cm and its diagonal is 5 cm. Its surface area is :