The perimeter of a rectangle is twice the sum of the length and width:
P = 2(L + W)
Since we are given L >= 50 ft and P = 140 ft:
140 >= 2(50 + W)
70 >= 50 + W
20 >= W
Therefore, the width is less than or equal to 20 ft.
(The maximum area is 50 x 20 = 1000 ft^2.)