Please please help i really need this.. The length of a rectangular fenced enclosure is 12 feet more than the width

If farmer Dan has 100 feet of fencing, find the dimensions of the rectangle with the largest perimeter that can be created using 100 feet of fencing.

Length = 31 ft
width = 19 ft

Assume that the width of the rectangle is w.
We are given that the length is 12 ft more than the width. This means that the length of the rectangle is w + 12

The perimeter of the rectangle in this case would be:
perimeter = 2 (length + width)
perimeter = 2 (12 + w + w)
perimeter = 24 + 4w

Assume that Dan would use all 100 ft of fencing to surround the yard. This would mean that the largest perimeter is 100 ft.

Therefore:
perimeter = 24 + 4w
100 = 24 + 4w
4w = 100 - 24
4w = 76
w = 19 ft

Since we have calculated that the width of the yard is 19 ft, we can substitute to get the length as follows:
length = 12 + w
length = 12 + 19
length = 31 ft

Just divide the x axis (the top) by 2 or multiply the y axis (the bottom) by 2

The answer would be a