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Explanation:
The area of the garden only (ignore the circular pathway) is approximately
A = pi*r^2
A = 3.14*20^2
A = 1256
The area of the garden plus the path is approximately
A = pi*r^2
A = 3.14*21^2
A = 1384.74
Notie how I added on 1 meter to increase the radius to 21
Subtract the two circle areas to get the area of the circular ring.
1384.74 - 1256 = 128.74
The units for all of the areas mentioned are "square meters".