ANSWER
The field has an area of

Step-by-step explanation
The total fencing around a square field gives the total distance around the square field.
The total fencing around the field being

yards means, the perimeter is 80 yards.
Recall that the perimeter of a square is given by the formula,

This implies that,

We divide both sides by 4 to get,

This implies that

We now obtain the area of the square by using the formula,

