The radius of a wheel of a car is $21 \, cm$. If it makes $800$ rotations per minute,find the speed of the car in $km/h$.

In the figure,arcs are drawn by taking vertices $A, B$ and $C$ of an equilateral triangle of side $10 \, cm$ as centers to intersect the sides $BC, CA$ and $AB$ at their respective mid-points $D, E$ and $F$. Find the area of the shaded region (Use $\pi = 3.14$) (in $cm^2$).

As shown in the diagram, rectangle $ABCD$ is a metal sheet in which $CD = 20 \, cm$ and $BC = 14 \, cm$. From it, a semicircle with diameter $\overline{BC}$ and a sector with centre $A$ and radius $AD$ is cut off. Find the area of the remaining sheet in $cm^2$.

The circumference of a circle with radius $8.4\,cm$ is $\ldots \ldots \ldots \ldots cm$.

Find the area of the shaded region in the given figure.

In a circle with radius $8.4 \, cm$,a minor arc subtends an angle of $60^{\circ}$ at the centre. Find the area of the minor sector and the major sector corresponding to this arc.