The table should be completed with the length and area for each width as follows;
width (feet) length (feet) area (square feet)
10 100 1000
30 60 1800
40 40 1600
w 120 - 2w

In Mathematics and Geometry, the perimeter of a rectangle can be calculated by using this mathematical equation (formula);
P = 2(L + W)
Where:
- P represent the perimeter of a rectangle.
- W represent the width of a rectangle.
- L represent the length of a rectangle.
Since 120 feet of fencing material was used to enclose three sides of the play area, it implies there are only 3 sides;
120 = L + 2W
L = 120 - 2W
In order to maximize the area, the width must be 30 feet and the length must be 60 feet;
120 = L + 2W
120 = 60 + 2(30)
120 = 120
For the area, we have;
Area of rectangle, A = LW
A = (120 - 2W)W

By taking the first derivative of the area function and equating to zero, we have;
A' = 120 - 4W
0 = 120 - 4W
4W = 120
W = 120/4 = 30 feet.
When W is 30 feet, the length and area are given by;
L = 120 - 2(30)
L = 60 feet.
A = 30 × 60
A = 1800 sq. ft.
When W is 10 feet, the length and area are given by;
L = 120 - 2(10)
L = 100 feet.
A = 100 × 10
A = 1000 sq. ft.
When W is 40 feet, the length and area are given by;
L = 120 - 2(40)
L = 40 feet.
A = 40 × 40
A = 1600 sq. ft.
When W is w feet, the length and area are given by;
L = 120 - 2(w)
L = (120 - 2w) feet.
A = (120 - 2w) × w
A =
sq. ft.