$\text{I.}$

$\text{P}=\left({\left(9\text{cm}\right)}^2-{\left(5\text{cm}\right)}^2\right)\cdot \pi =\left(81{\text{cm}}^2-25{\text{cm}}^2\right)\cdot \pi =56\pi {\text{cm}}^2$

$\text{P}=56{\text{cm}}^2\cdot 3,1=56{\text{cm}}^2\cdot \left(3+0,1\right)=56{\text{cm}}^2\cdot 3+56{\text{cm}}^2\cdot 0,1=$

$=168{\text{cm}}^2+5,6{\text{cm}}^2=173,6{\text{cm}}^2$

 

$\text{II.}$

$\text{P}=\left({\left(4\text{cm}\right)}^2-{\left(1\text{cm}\right)}^2\right)\cdot \pi =\left(16{\text{cm}}^2-1{\text{cm}}^2\right)\cdot \pi =15\pi {\text{cm}}^2$

$\text{P}=15{\text{cm}}^2\cdot 3,1=15{\text{cm}}^2\cdot \left(3+0,1\right)=15{\text{cm}}^2\cdot 3+15{\text{cm}}^2\cdot 0,1=$

$=45{\text{cm}}^2+1,5{\text{cm}}^2=46,5{\text{cm}}^2$