The diameter of the centerline of the walkway is 13 ft, so the circumference of that circle is 13π feet. The area of the walk is the product of its centerline length and its width:
A = (13π ft)·(3 ft) = 39π ft² ≈ 122.5 ft²
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You can get there also by subtracting the area of the fountain circle from the area of the circle containing walkway and fountain.
... A = (π/4)d² . . . . . . . area for a circle of diameter d
... A = (π/4)((16 ft)² -(10 ft)²) = 39π ft² . . . . . . area difference of interest
