[tex]\begin{cases}A_{\square} = 25\, m^2 \\ A_{\square} =l^2\\ P_{\square} = 4l \end{cases}\Bigg| \Rightarrow l^2 = 25\, m^2 \,\Leftrightarrow \, l =\sqrt{25\, m^2} \, \Leftrightarrow \, l = 5\, m\\\\\\\Rightarrow P_{\square} = 4\cdot 5 \, m \, \,\Leftrightarrow\,\,\boxed{P_{\square} = 20\, m}[/tex]
