How many balls of radius $0.5\, cm$ can be produced by melting a metallic cylinder with radius $4\, cm$ and height $3\, cm$?

The base of a cone is hemispherical. The radius of the cone is $15 \, cm$ and the total height of the solid is $55 \, cm$. Find the volume of this solid (in $cm^3$).

$A$ tent is cylindrical at the base and conical at the top. Its radius is $1.2\, m$. The height of the cylindrical part is $4\, m$ and the height of the conical part is $3.5\, m$. How many square metres of cloth is used to make the tent?

$A$ metallic sphere with radius $18 \,cm$ is melted and recast to produce cylinders with radius $3 \,cm$ and height $12 \,cm$. Find the number of cylinders produced.

The radii of two $10 \, cm$ high metallic cylinders are $3.5 \, cm$ and $7 \, cm$. These cylinders are melted and recast to produce a cylinder with height $50 \, cm$. Find the radius of this new cylinder (in $cm$).

The volume of a cylinder is $550 \, cm^{3}$ and its radius is $5 \, cm$. Then,the height of the cylinder is $\ldots \ldots \ldots \, cm$.