1)[tex] A_{f} = \frac{ l^{2} \sqrt{3} }{4} \\
9 \sqrt{3} = \frac{ l^{2} \sqrt{3} }{4} \\
l^{2} = \frac{9 \sqrt{3}*4 }{ \sqrt{3} } \\
l^{2} = 36 \\
l=6 \\
S_{m} =6l \\
S_{m} =6*6=36[/tex]
2)[tex]l_{b} =4 \\
P_{m} =40 \\
m_{l} =? \\
P_{m} =4 l_{b} +4 m_{l} \\
40=4*4+4 m_{l} \\
40=16+4 m_{l} \\
4 m_{l}=24 \\
m_{l}=6[/tex]