II) 2.
[tex]\it DE||BC\ \stackrel{T.f.a.}{\Longrightarrow}\ \dfrac{AB}{AD}=\dfrac{BC}{DE}=\dfrac{AC}{AE} \Rightarrow \dfrac{20}{4}=\dfrac{25}{DE}=\dfrac{15}{AE} \Rightarrow\\ \\ \\ \Rightarrow \begin{cases} \it 5=\dfrac{25}{DE} \Rightarrow\it DE=5\ cm\\ \\ \it 5=\dfrac{15}{AE} \Rightarrow\it AE=3\ cm\end{cases}[/tex]
[tex]\it \mathcal{P}_{ADE}=AD+DE+AE=4+5+3=12\ cm[/tex]
