STEP 1: find side $ a $
To find side $ a $ use formula:
$$ d = \sqrt{ 2 } \cdot a $$After substituting $d = 6.7\, \text{cm}$ we have:
$$ 6.7\, \text{cm} = \sqrt{ 2 } \cdot a $$ $$ a = \dfrac{ 6.7\, \text{cm} }{ \sqrt{ 2 } } $$ $$ a \approx 4.7376\, \text{cm} $$STEP 2: find base area $ B $
To find base area $ B $ use formula:
$$ B = a^2 $$After substituting $a = 4.7376\, \text{cm}$ we have:
$$ B = \left( 4.7376\, \text{cm} \right)^{2} $$ $$ B = 22.445\, \text{cm}^2 $$