To find base area $ B $ use formula:
$$ B = \dfrac{ \sqrt{ 3 } \cdot a^2 }{ 4 } $$After substituting $a = 2\, \text{cm}$ we have:
$$ B = \dfrac{ \sqrt{ 3 } \cdot \left( 2\, \text{cm} \right)^{2} }{ 4 } $$ $$ B = \dfrac{ \sqrt{ 3 } \cdot 4\, \text{cm}^2 }{ 4 }$$ $$ B = \dfrac{ 4 \sqrt{ 3 }\, \text{cm}^2 }{ 4 }$$ $$ B = \sqrt{ 3 }\, \text{cm}^2 $$