\(Area\ of\ a\ rectangle:A_{\fbox{ }}=9m\times4m=36m^2\\\\a-side\ of\ a\ square\\\\Area\ of\ a\ square:A_{\fbox{}}=a^2\\\\A_{\fbox{ }}=A_{\fbox{}}\Rightarrow a^2=36m^2\Rightarrow a=\sqrt{36m^2}\Rightarrow a=6m\\\\Perimeter\ of\ the\ square:P=4a\Rightarrow P=4\times6m=\boxed{24m}\\\\Diagonal\ of\ the\ square:d=a\sqrt2\Rightarrow d=\boxed{6\sqrt2\ m}\)