I must admit that when I saw the request on the calculator creation/2658/, which sounded like "calculate area by perimeter". I was a little surprised because it looked somewhat surreal.
Although, after some search on the Internet, I realized that the request just not complete, and often goes like this: "Calculate the area of a rectangle if its perimeter is equal to X and it is known that ..." - and there are different things that may be known. These things lead us to a solution—for example, the length of one of the sides or the aspect ratio. The calculator below calculates the rectangle area, depending on what else is known apart from the perimeter. I dedicate it to all students.