Am I stupid? (What is the circumference?)

Please, tag anwsers as spoilers before posting, I still didn't crack it.

@LukeAlmighty the left and right side are 6 each, but we can't say much for the top and bottom sides, because we don't know how much the 4 and 5 sections overlap.
The top and bottom sides must be longer than 5 and shorter than 9 each.
So the circumference (or perimeter) is in the range 22<P<30

@critical
I hate to inform you, that there is enough information to finish the task.

@LukeAlmighty top and bottom are 4+5-x= 9-x
So P=2*6 + 2*(9-x) = 12+18-2*x = 30-2*x
0<x<4
What am I missing?

@critical
Top and botom are both 9-x, but there is also two overlaps, both x long, so the x cancels itself out.

Visually, you can place the 4cm and 5cm walls next to each other, creating a gap on the top the exact length of the horisontal line in the middle.