To find side $ a $ use formula:
$$ r = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$After substituting $ r = 16 $ we have:
$$ 16 = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$ $$ \sqrt{ 3 } \cdot a = 16 \cdot 2 $$ $$ \sqrt{ 3 } \cdot a = 32 $$ $$ a = \dfrac{ 32 }{ \sqrt{ 3 } } $$ $$ a = \frac{ 32 \sqrt{ 3}}{ 3 } $$