$A$ metallic ball of radius $9 \,cm$ is melted and recast into three metallic balls. If the radii of two balls are $1 \,cm$ and $6 \,cm$,find the radius of the third ball (in $cm$).

Curved surface area of a cylinder $= \ldots \ldots \ldots$

Total surface area of a hemisphere $= \dots$

The length and breadth of a cuboid are $30\, cm$ and $25\, cm$. If the total surface area of the cuboid is double the lateral surface area of the cuboid,find its height and volume.

The length of a metal hollow cylinder is $70\, cm$. If the radius of the hollow inside it is $10\, cm$ and the metal thickness is $1\, cm$,find the difference between the areas of the outer and inner curved surfaces.

The water for a factory is stored in a hemispherical tank whose internal diameter is $14\, m$. The tank contains $50$ kilolitres of water. Water is pumped into the tank to fill it to its capacity. Calculate the volume of water pumped into the tank. (in $, m^{3}$)