Answer: Choice B) 20*sqrt(2) ft
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I'm assuming that the A stands for area. If so, then A = 200 is given to us
Plug this into the formula to get....
d = sqrt(4*A)
d = sqrt(4*200)
d = sqrt(800)
d = sqrt(400*2)
d = sqrt(400)*sqrt(2)
d = 20*sqrt(2)