The total surface area of a cube is $864 \, cm^2$. Then its edge is $\ldots \ldots \ldots \, cm$.

There are two boxes of metal sheet. The length,width,and height of a cuboidal box are $30 \, cm$,$25 \, cm$,and $20 \, cm$ respectively. $A$ cubical box has each edge of $25 \, cm$. Find out which box requires more metal sheet and by how many $cm^2$?

$A$ patient in a hospital is given soup daily in a cylindrical bowl of diameter $7 \, cm$. If the bowl is filled with soup to a height of $4 \, cm$, how much soup does the hospital have to prepare daily to serve $250$ patients?

The length,breadth,and height of a room are $5\, m$,$4\, m$,and $3\, m$ respectively. Find the cost of whitewashing the walls of the room and the ceiling at the rate of $Rs. 7.50$ per $m^2$.

The edge of a cube is $35\, cm$. Find the total surface area of the cube (in $cm^2$).

Find the curved surface area and the total surface area of a hemisphere with a radius of $2.1 \, m$.