If you Walk perimeter of 3 acres equals how many miles walked?

You will have walked about 10.92 miles in perimeter.

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That is a total rubbish answer. An area does not and cannot define a perimeter. An area of 3 acres can comprise an extremely thin strip stretching millions of miles. So the perimeter would also run to millions of miles. And if the strip was thinner, it could be billions of miles or trillions, etc.