Among all the rectangles whose perimeters are 100 ft, find the dimensions of the one with maximum area

A rectangle can also a square, which means they can have four equal sides and it would still be a rectangle, so you can take 100, divide it by 4 and each side will equal 25 ft. and when you try to find the area it will be 625 ft^2 and that is the biggest area possible because if you try any other combination, the area becomes less and less.