To find side $ a $ use formula:
$$ R = \dfrac{ \sqrt{ 3 } \cdot a }{ 3 } $$After substituting $R = 61.62\, \text{cm}$ we have:
$$ 61.62\, \text{cm} = \dfrac{ \sqrt{ 3 } \cdot a }{ 3 } $$ $$ \sqrt{ 3 } \cdot a = 61.62\, \text{cm} \cdot 3 $$ $$ \sqrt{ 3 } \cdot a = 184.86\, \text{cm} $$ $$ a = \dfrac{ 184.86\, \text{cm} }{ \sqrt{ 3 } } $$ $$ a \approx 106.729\, \text{cm} $$