To warn ships for underwater rocks, a lighthouse spreads a red coloured light over a sector of angle $80°$ to a distance of $16.5 \mathrm{km}$. Find the area of the sea over which the ships are warned. $(\text{Use} = 3.14)$

In the adjoining figure, $AB \text{and} CD$ are respectively arcs of two concentric circles with centre $O$ of a radii $7 \mathrm{cm} \text{and} 3.5 \mathrm{cm}$. If $\angle AOB = 30°$, find the area of the shaded region.

In the adjoining figure, two concentric circles with centre O have radii 21 cm and 42 cm. If ZAOB = 60°, find the area of the shaded region.

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 figure, arcs have been down of radius $21 \mathrm{cm}$ each with vertices $A, B, C$ and $D$ of quadrilateral $ABCD$ as centres. Find the area of the shaded region.