We have to find the area which multiplied by 160 gives 1 square mile.
We know that : 1 square mile = 0.3867 sq km.
So it is not from the metric system.
The acre is exactly 1/640 of a square mile. 1/4 of the square mile is 160 acres.
1 sq mile = 640 acres
1 sq mile = 160 * 4 acres
Answer: 4 acres.
