Find the volume of a sphere of radius $2.1 \, cm$. (in $cm^3$)

The radius of a sphere is $14 \, cm$. Find its surface area (in $cm^2$).

Two solid spheres made of the same metal have weights $5920\, g$ and $740\, g$ respectively. Determine the radius of the larger sphere,if the diameter of the smaller one is $5\, cm$. (in $cm$)

How many square metres of canvas is required for a conical tent whose height is $3.5 \, m$ and the radius of the base is $12 \, m$ (in $, m^{2}$)?

The edges of three of the four cubes are $1\, cm, 9\, cm$ and $10\, cm$ respectively. If the total volume of two cubes with $9\, cm$ edge and $10\, cm$ edge is equal to the volume of the remaining two cubes,find the edge of the fourth cube in $cm$.

$A$ cylindrical tube open at both ends is made of an iron sheet which is $2 \, cm$ thick. If the outer diameter is $16 \, cm$ and its length is $100 \, cm$, find how many cubic centimeters of iron have been used in making the tube? (in $cm^3$)