In a circle,the area of a sector formed by two radii perpendicular to each other is $38.5 \, cm^2$. Find the radius of the circle (in $cm$).

In a circle with radius $30\,cm$,a minor arc subtends an angle of measure $60^{\circ}$ at the centre. Then,the area of the minor sector formed by that arc is $\ldots \ldots \ldots \ldots$ $cm^{2}$. $(\pi = 3.14)$

The radius of a circle is $12 \, cm$. Find its circumference and area $(\pi = 3.14)$.

$A$ calf is tied with a rope of length $6 \,m$ at the corner of a square grassy lawn of side $20 \,m$. If the length of the rope is increased by $5.5 \,m$,find the increase in area of the grassy lawn in which the calf can graze. (in $m^2$)

From a circular metallic sheet with radius $21\, cm$,a regular hexagon of side $21\, cm$ is cut off. Find the area of the remaining sheet. $(\sqrt{3} = 1.73)$ (in $cm^2$)

The circumference of a circle is $251.2 \, cm$. Find its diameter. $(\pi = 3.14)$ (in $cm$)