To find area $ A $ use formula:
$$ A = \dfrac{ d_1 \cdot d_2 }{ 2 } $$After substituting $d_1 = 12 \sqrt{ 3 }\, \text{cm}$ and $d_2 = 6 \sqrt{ 3 }\, \text{cm}$ we have:
$$ A = \dfrac{ 12 \sqrt{ 3 }\, \text{cm} \cdot 6 \sqrt{ 3 }\, \text{cm} }{ 2 }$$$$ A = \dfrac{ 216\, \text{cm}^2 }{ 2 } $$$$ A = 108\, \text{cm}^2 $$