If you visualize the problem, there are two concentric circles, the pool, and the pool plus the walkway. So, we have to subtract the area of these two concentric circles to find the walkway.
Bigger circle: Pool plus walkway
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diameter = 18 + 4(2) -- this is because there is 2 ft of walkway at each far end
diameter = 26 ft
Area = pi*(26/2)^2
Area = 530.93 ft2
Smaller circle:pool
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diameter = 18 ft
Area = pi*(8/2)^2
Area = 50.27 ft2
Area of walkway
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A = 530.93 - 50.27
A = 480.66 ft2
Then the cost would be
Cost = $4.25 * 480.66
Cost = $2,042.81
