To find base area $ B $ use formula:
$$ B = \dfrac{ \sqrt{ 3 } \cdot a^2 }{ 4 } $$After substituting $ a = 1.6 $ we have:
$$ B = \dfrac{ \sqrt{ 3 } \cdot 1.6^2 }{ 4 } $$ $$ B = \dfrac{ \sqrt{ 3 } \cdot 2.56 }{ 4 }$$ $$ B = \dfrac{ 4.4341 }{ 4 }$$ $$ B = 1.1085 $$