The area of a ring whose outer and inner radii are respectively $20 \, cm$ and $15 \, cm$ is? (in $cm^2$)

$A$ bed of roses is shaped as shown in the figure below. In the centre is a square and on each side there is a semi-circle. The side of the square is $21 \, m$. If each rose plant needs $6 \, m^{2}$ of space,then the number of plants in the bed is?

If a wire is bent into the shape of a square,then the area of the square is $81 \, cm^2$. When the wire is bent into a semi-circular shape,the area of the semi-circle will be (in $cm^2$):

What will be the area of a circle with circumference equal to $22 \, cm$? (in $sq \, cm$)

In a shower,$10\, cm$ of rain falls. What will be the volume of water that falls on $1$ hectare area of ground? (in $m^3$)

In the given figure,$QRST$ is a square. If the area of each circle is $2 \pi$,then find the area of square $QRST$?