If the side of a cube is increased by $100 \%$,its volume is increased by (in $\%$)

Three solid spheres have their radii $r_{1}, r_{2}$ and $r_{3}$. The spheres are melted to form a single solid sphere of a bigger radius. The radius of the new sphere is:

$A$ cylindrical jar of diameter $24\, cm$ contains water to a height of $30\, cm$. $A$ spherical steel ball is dropped into the jar and the level of the water rises by $67.5\, mm$. The diameter of the ball is......$cm$.

$A$ rectangular tin sheet is $12 \, cm$ long and $5 \, cm$ broad. It is rolled along its length to form a cylinder by making the opposite edges just touch each other. Then the volume of the cylinder is

The radius of a cylinder is made twice as large. How should the height be changed so that its volume remains unchanged?

$A$ rectangular plot,$36 \, m$ long and $28 \, m$ broad,has two concrete roads $5 \, m$ wide running in the middle of the park,one parallel to the length and the other parallel to the breadth. What would be the total cost of gravelling the plot,excluding the area covered by the roads,at ₹ $3.60$ per $m^{2}$? (in $Rs.$)