\[Страница\ 86.\]
\[\boxed{\mathbf{4}.}\]
\[4 \cdot (6 + 7 + 9) = 4 \cdot 20 =\]
\[= 80\ (см) - длина\ всех\ ребер.\]
\[Ответ:80\ см.\]
\[\boxed{\mathbf{5}.}\]
\[\textbf{а)}\ Вершины:M;N;K;P;A;B;C;\]
\[\text{D.}\]
\[Ребра:AM;MN;NK;KP;MP;KC;\]
\[PD;CD;AD;AB;BC;BN.\ \]
\[Грани:ABCD;MNKP;ABNM;\]
\[CDPK;AMPD;BCKN.\]
\[\textbf{б)}\ AMPD;ABNM.\]
\[\textbf{в)}\ MP;PK;PD.\]
\[\textbf{г)}\ M;MP.\]
\[\textbf{д)}\ PK;AB;CD.\]
\[\textbf{е)}\ NK;AD;BC.\]
\[\textbf{ж)}\ ABNM.\]
\[\textbf{з)}\ ABCD.\]
\[\textbf{и)}\ BCKN.\]
\[\boxed{\mathbf{6}.}\]
\[Ответ:3).\]