To find side $ a $ use formula:
$$ r = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$After substituting $ r = 43 $ we have:
$$ 43 = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$ $$ \sqrt{ 3 } \cdot a = 43 \cdot 2 $$ $$ \sqrt{ 3 } \cdot a = 86 $$ $$ a = \dfrac{ 86 }{ \sqrt{ 3 } } $$ $$ a = \frac{ 86 \sqrt{ 3}}{ 3 } $$