$a)L=2\cdot \pi \cdot 2,5cm=5\pi cm$

$b)L=11cm\cdot \pi =11\pi cm$

$c)P=\pi \cdot {\left(18cm\right)}^2=324\pi c{m}^2$ $c)P=\pi \cdot {\left(18cm\right)}^2=324\pi c{m}^2$

$d)r=20cm:2=10cm$

$P=\pi \cdot {\left(10cm\right)}^2=100\pi c{m}^2$

$e)2\pi r=30\pi cm\Rightarrow r=30\pi cm:2\pi =15cm$

$f)\pi r^2=49\pi c{m}^2\Rightarrow r^2=49c{m}^2\Rightarrow r=\sqrt{49c{m}^2}=7cm\Rightarrow d=2\cdot 7cm=14cm$

$g)2\pi r=60\pi cm\Rightarrow r=60\pi cm:2\pi =30cm$

$P=\pi \cdot {\left(30cm\right)}^2=900\pi c{m}^2$

$h)\pi r^2=144\pi c{m}^2\Rightarrow r^2=144c{m}^2\Rightarrow r=\sqrt{144c{m}^2}=12cm$

$L=2\cdot \pi \cdot 12cm=24\pi cm$