$PQ$ is the diameter of the semicircle with centre $O. OR$ is the diameter of the small circle inscribed in it. Find the shaded area if $PQ=21 cm$. 

 

The quadrants shown in the figure given below are each of radius $7 \mathrm{cm}$. Calculate the area of the shaded portion.

Two small circles touching each other externally and of radius $6 cm$ are inscribed in a circle. Find the shaded area.

[Take $\mathrm{\pi }=\frac{22}{7}$]

Two semicircles and one circle of same radius $5 cm$ are inscribed in a rectangle. Find the area of shaded region. [Take $\mathrm{\pi }=\frac{22}{7}$]

 Triangle $PQR$ is inscribed in a semicircle. $PQ=PR=7 cm$. Find the shaded area.

. Triangle $ABC$ is inscribed in a semicircle. $AB=12 cm, BC=16 cm$. Find $AC$.. [Take $\mathrm{\pi }=3.14$]
 

. Triangle $ABC$ is inscribed in a semicircle. $AB=12 cm, BC=16 cm$. Find the shaded area. [Take $\mathrm{\pi }=3.14$]