[tex]\displaystyle\\
\text{Daca } \frac{AB}{MN}= \frac{3}{2}~~~ \Longrightarrow ~~~ \frac{P_{ABC}}{P_{MNP}}= \frac{3}{2} \\ \\
\Longrightarrow ~~~P_{MNP}=\frac{P_{ABC}}{\frac{3}{2}}=\frac{24+20+22}{\frac{3}{2}}=\\\\
=\frac{66}{\frac{3}{2}}=66\times \frac{2}{3}=22\times 2= \boxed{44~cm}[/tex]