Given:
The radius of inner circle = 13 yd.
The width of the shaded region = 8 yd
To find the area of the shaded region.
Now,
The radius of the outer circle = 13+8 yd = 21 yd
Formula
The area of a circle of radius r unit is 
 sq unit.
 sq unit.

where, 
 = The area of the shaded region
 = The area of the shaded region
 = Area of the outer region
 = Area of the outer region 
 = Area of the inner region
= Area of the inner region
Now,

 
 
 
 


 sq yd
 sq yd
And,
 
 
 
 
 
 


 sq yd
 sq yd
Therefore,
 sq yd
 sq yd
 sq yd
 sq yd
Hence,
The area of the shaded region 854.08 sq yd.