By definition the area of a rectangle is:
A = w * l
The perimeter is:
P = 2w + 2l
Where,
w: width
l: long
Substituting values:
300 = w * l
80 = 2w + 2l
Solving the system of equations we have:
l = 30 m
w = 10 m
Answer:
The length and width of the field are:
l = 30 m
w = 10 m