Find the surface area of a sphere with a diameter of $21\, cm$ (in $cm^2$).

Curved surface area of a cone $= \dots$

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 $cm^3$)

Lateral surface area of a cuboid $= \ldots \ldots \ldots$

The curved surface area of a cylinder is $4400 \, cm^2$ and its base has a radius of $14 \, cm$. Find the volume of the cylinder in $cm^3$.