A water body is of cuboidal shape of (Cuboid is a right-angled parallelepiped). Its length $20 \mathrm{m}$. When $18 kl$ water is taken out of the water body, its level goes down by $15 \mathrm{cm}$. Find the breadth of the water body.

Mary wants to keep her Christmas tree in a wooden box covered with coloured paper. She wants to know how much paper she needs to buy. The above mentioned box is $80 \mathrm{cm}$ long, $40 \mathrm{cm}$ wide and $20 \mathrm{cm}$ high. And if the paper is $40 \mathrm{cm}$ square sheets then how many sheets are needed.