Answer: Choice A) about 69.53 m^2
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Work Shown:
A = area of the square
A = side*side
A = 18*18
A = 324 square meters
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B = area of the circle
B = pi*r^2
B = pi*9^2 ..... note that the radius is half the diameter
B = 81pi
B = 254.469004940773
B = 254.4690 square meters
I used the calculator's stored version of pi to compute that approximate value.
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C = area of shaded region
C = A - B
C = 324 - 254.4690
C = 69.531
C = 69.53 square meters
So that points us to choice A as the final answer.
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Side note: The shaded region is about C/A = (69.531)/(324) = 0.2146 = 21.46% of the square's area. So this is the approximate chances of landing in the shaded area if you randomly threw a dart.