To find area $ A $ use formula:
$$ A = 4 \cdot r^2 \cdot \pi $$After substituting $r = 2.5\, \text{mm}$ we have:
$$ A = 4 \cdot \left( 2.5\, \text{mm} \right)^{2} \cdot \pi $$ $$ A = 25\, \text{mm}^2 \cdot \pi $$ $$ A = 25\, \text{mm}^2 \cdot \pi $$