Question

A rectangular field is 80 meters wide and 125 meters long.

Answer 1

Perimeter of the rectangle is 2*(80+125)=410
The rectangle having the biggest area given the same perimeter is a square. So we need to go "the other way" -- find the rectangle with larger side ratio. 200 m and 5 m is a good example.

The area of the first rectangle: $80 m \times 125 m =10000 m^2$
The area of the second rectangle : $200 m \times 5 m = 1000 m^2$ (10 times smaller).