[tex]\it \mathcal{P}=2(L+\ell) \Rightarrow 80=2(L+\ell)\bigg|_{:2} \Rightarrow L+\ell=40 \Rightarrow L=40-\ell\ \ \ \ \ (1)\\ \\ \\ L > \ell\ de\ 4\ ori \Rightarrow L=4\ell\ \ \ \ \ (2)\\ \\ \\ (1),\ (2) \Rightarrow 4\ell=40-\ell\bigg|_{+\ell} \Rightarrow 5\ell=40\bigg|_{:5} \Rightarrow \ell=8\ m\ \ \ \ \ (3)\\ \\ \\ (2),\ (3) \Rightarrow L=4\cdot8 \Rightarrow L=32\ m[/tex]
