You can't. Knowing just the perimeter doesn't tell you the area, and
knowing just the area doesn't tell you the perimeter.
If you only know the area, there are an infinite number of different
rectangles, all with different dimensions and perimeters, that all have
the same area. Let me show you what I mean:
Length x width . . . Area . . . Perimeter
1 x 64 . . . . . . . . 64 . . . . . 130
2 x 32 . . . . . . . . 64 . . . . . . 68
4 x 16 . . . . . . . . 64 . . . . . . 40
8 x 8 . . . . . . . . . 64 . . . . . . 32
6.4 x 10 . . . . . . . . 64 . . . . . . 32.8
3.2 x 20 . . . . . . . . 64 . . . . . . 46.4
0.16 x 400 . . . . . . . 64 . . . . . 800.32
See what I mean ?