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The area of the circular fountain is = = 615.44 square feet.
As you understand, 14 here is the radius of the fountain.
The radius of the outer circle is 14+3.5 = 17.5 feet, and the area of that circle is = 961.625 square feet.
The difference 961.625 - 615.44 = 346.185 square feet is the area of the sidewalk.
To find the number of bags of concrete, multiply this area by the number 0.8
N = 346.185*0.8 = 432.7 = 276.9 = 270 bags of concrete (rounded to the next greater integer). ANSWER
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