$A$ cylindrical roller $2.5\, m$ in length and $1.75\, m$ in radius,when rolled on a road,was found to cover an area of $5500\, m^{2}$. How many revolutions did it make?

Surface area of a sphere $= \ldots \ldots.$

$A$ heap of wheat is in the form of a cone whose diameter is $42 \, m$ and height is $20 \, m$. The heap is to be covered by canvas to protect it from rain. If the price of canvas is $₹ 75$ per $m^2$,find the cost of the canvas required.

In $\triangle ABC$,$\angle B = 90^{\circ}$,$AB = 28 \, cm$,and $BC = 21 \, cm$. If the triangle is revolved about the side $AB$,find the curved surface area of the cone so obtained. Similarly,if the triangle $ABC$ is revolved about the side $BC$,find the curved surface area of the cone so obtained.

State whether the following statement is true or false:
The radius of a cone can be $3 \, cm$,slant height $4 \, cm$,and height $5 \, cm$.

$1$ hectare $= \ldots \ldots \text{ } m^{2}$