If the perimeter is 72 inches, what is the area of the poster

You can't tell.  The perimeter doesn't tell you the area, and the
area doesn't tell you the dimensions.

Here's a little example.  ALL of the rectangles on this list have
the same perimeter ... 72 inches:

1 x 35 . . . . . Area = 35 square inches
2 x 34 . . . . . Area =  68 square inches
3 x 33 . . . . . Area =  99 square inches
4 x 32 . . . . . Area =  128 square inches
5 x 31 . . . . . Area =  155 square inches
6 x 30 . . . . . Area =  180 square inches
10 x 26 . . . . . Area = 260 square inches
15 x 21 . . . . . Area = 315 square inches
18 x 18 . . . . . Area = 324 square inches .

See what I mean ?