To find side $ l $ use Pythagorean Theorem:
$$ r^2 + h^2 = l^2 $$After substituting $r = 3.6\, \text{cm}$ and $h = 4.1\, \text{cm}$ we have:
$$ \left( 3.6\, \text{cm} \right)^{2} + \left( 4.1\, \text{cm} \right)^{2} = l^2 $$ $$ 12.96\, \text{cm}^2 + 16.81\, \text{cm}^2 = l^2 $$ $$ l^2 = 29.77\, \text{cm}^2 $$ $$ l = \sqrt{ 29.77\, \text{cm}^2 } $$$$ l = 5.4562\, \text{cm} $$