What is the area of a rectangle with a perimeter of 30cm?

Let h and w equal the dimensions of the rectangle and A equal its area

2h + 2w = 30

The perimeter of the rectangle is the sum of its sides, two widths and two heights

h*w = A

The formula for the area of a rectangle

We have two equations but three unknown variables. Without more information about this rectangle, it is impossible to solve for the area from the perimeter alone unless this rectangle was specified as being a square (which gives us a third equation, b = h )