Asection of land has an area of 1 square mile and contains 640 acres. determine the number of square meters in an acre

1 mile = 1760 yards
1 squre mile = 1760^2 yd^2 = 3097600 yd^2
This means that
Each acre has (3097600 yd^2/ sq. mile ) / (640 acres/sq. mile(= 4840 yd^2 / acre

Also, we know that 1 inch = 2.54 cm exactly. 
Therefore
1 yd = 3*12*2.54 cm = 91.44 cm = 0.9144 m
1 yd^2 = (0.9144 m)^2 = 0.83612736 m^2

Using the conversion from acre to sq yards,
1 acre=4840 yd^2
=4840 yd^2 * 0.83612736 m^2 / yd^2
= 4046.8564224 m^2

1 acre = 4046.8564224 m^2