The length in feet is (x - 80) feet
Solution:
The area in square feet of a rectangular field is

The width, in feet, is x - 60
To find: length in feet
The area of rectangle is given as:

Now we can simplify area
area =

-140x can be rewritten as -80x - 60x

Taking "x" as common from first two terms and -60 as common from last two terms
area = x(x - 80) -60(x - 80)
Taking (x - 80) as common term
Area = (x - 80)(x - 60)
Substitute area = (x - 80)(x - 60) and width = (x - 60)

Cancelling (x - 60)
length = (x - 80)
Thus the length in feet is (x - 80) feet