Question 509424
The walkway and pool are circular, so the inside circumference of the walkway is less than the outside circumference.  So, you can take the area of the inner circle (which is the pool, actually) and subtract it from the area of the outer circle.
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pi*r^2 = area of the pool
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pi*(r+3)^2 = area of the pool + walkway
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pi*r^2 = pi*(r+3)^2 - 198
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pi*r^2 = pi*(r^2 +6r +9) - 198
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pi*r^2 = pi*r^2 + pi*6r + pi*9 -198
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0 = pi*6r + pi*9 -198
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pi*6r + pi*9 = 198
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pi*(6r + 9) = 198
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6r + 9 = 198/pi = 63.0253575
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6r = 63.0253575 -9 = 54.0253575
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r = 54.0253575/6
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r = 9.00422624
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r+3 = radius to outer edge of walkway
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r+3 = 12.00422624
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inner area = pi*(9.00422624^2)
inner area = 254.708049
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outer area = pi*(12.00422624^2)
outer area = 452.708049
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walkway area = 452.708049 - 254.708049 = 198
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Correct.
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Answer:  The radius of the pool is 9.00422624 or about 9 meters.
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Done.