To find radius $ r $ use formula:
$$ A = 4 \cdot r^2 \cdot \pi $$After substituting $A = 5\, \text{cm}$ we have:
$$ 5\, \text{cm} = 4 \cdot r^2 \cdot \pi $$ $$ r^2 \cdot \pi = \dfrac{ 5\, \text{cm} }{ 4 } $$ $$ r^2 \cdot \pi = \frac{ 5 }{ 4 }\, \text{cm} $$ $$ r = \sqrt{ \frac{ \frac{ 5 }{ 4 }\, \text{cm} }{\pi} } $$ $$ r \approx 0.6308 $$