[tex]P_{ABCD} =81~cm^{2} ~~\land~~P_{ABCD} =a^{2} ~~\Rightarrow ~~a^{2} =81~cm^{2}\\\\a^{2} =81~cm^{2}~~\land~~a > 0~~\Rightarrow ~~a=9~cm\\\\\\P_{HBIF} =9~cm^{2} ~~\land~~P_{HBIF} =b^{2} ~~\Rightarrow ~~b^{2} =9~cm^{2}\\\\b^{2} =9~cm^{2}~~\land~~b > 0~~\Rightarrow ~~b=3~cm[/tex]
[tex]P_{D E F G } =(6~cm)^{2} \\\\P_{D E F G } =36~cm^{2} \\\\Obw_{AHFE} =2\cdot 6~cm + 2\cdot 3~cm\\\\Obw_{AHFE} =18~cm\\\\Ad.1~~B.~~36~cm^{2} \\\\Ad.3~~C.~~18~cm[/tex]
