STEP 1: find side $ a $
To find side $ a $ use formula:
$$ d = 2 \cdot a $$After substituting $ d = 12 $ we have:
$$ 12 = 2 \cdot a $$ $$ a = \dfrac{ 12 }{ 2 } $$ $$ a = 6 $$STEP 2: find area $ A $
To find area $ A $ use formula:
$$ A = \dfrac{ 3 \sqrt{ 3 } \cdot a^2 }{ 2 } $$After substituting $ a = 6 $ we have:
$$ A = \dfrac{ 3 \sqrt{ 3 } \cdot 6^2 }{ 2 } $$ $$ A = \dfrac{ 3 \sqrt{ 3 } \cdot 36 }{ 2 }$$ $$ A = \dfrac{ 108 \sqrt{ 3 } }{ 2 }$$ $$ A = 54 \sqrt{ 3 } $$