The maximum possible area given a constant amount of material for a quadrilateral will always be a square.
For example if the material for the perimeter is 64 we can form a rectangle that is 22 by 10 which will have an area of 220 u^2.
However a square using the same amount of material will have sides of 64/4=16 and an area of 16^2=250 u^2
So in general the area is maximize the closer the sides are to being equal and minimized as the difference between the sides becomes greater. In the case of comparing the material, perimeter, of a rectangle to a square for the same amount of material the square will use less material than the rectangle.
A square can have a smaller perimeter and a greater area that a rectangle.
In the example above the rectangle had a perimeter of 64 u and an area of 220 u^2. If we made a square with just 60 u, it would have an area of 225 u^2.
