Surface Areas and Volumes question bank (Maths)

Mary wants to decorate her Christmas tree. She wants to place the tree on a wooden box covered with coloured paper with a picture of Santa Claus on it (see figure). She must know the exact quantity of paper to buy for this purpose. If the box has length,breadth,and height as $80 \, cm$,$40 \, cm$,and $20 \, cm$ respectively,how many square sheets of paper of side $40 \, cm$ would she require?

Hameed has built a cubical water tank with a lid for his house,with each outer edge $1.5\, m$ long. He gets the outer surface of the tank,excluding the base,covered with square tiles of side $25\, cm$ (see figure). Find how much he would spend on the tiles,if the cost of the tiles is $Rs. 360$ per dozen.