Find the area of a circle whose diameter is $14 \mathrm{m}$.

We know, 

Diameter = 2 x Radius
$\mathrm{Radius} =\frac{ \mathrm{Diameter}}{ 2 }=\frac{14 }{2 }=7 \mathrm{m}$  

The Area of a circle$= {\mathrm{\pi r}}^2$(Where $\mathrm{\pi }=\frac{22}{7}$)

$= \frac{22}{7} \times 7\times 7 = 154 {\mathrm{m}}^2$

So, the area of a circle is $154 {\mathrm{m}}^2.$