Use A(adj A) = |A| I

1. A.
   20
2. B.
   -200
3. C.
   200
4. D.
   -20

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1. A.
   $\begin{pmatrix} 60 & 0 & 0 \\ 0 & 60 & 0 \\ 0 & 0 & 60 \end{pmatrix}$
2. B.
   $\begin{pmatrix} 108 & 0 & 0 \\ 0 & 108 & 0 \\ 0 & 0 & 108 \end{pmatrix}$
3. C.
   $\begin{pmatrix} 20 & 0 & 0 \\ 0 & 20 & 0 \\ 0 & 0 & 20 \end{pmatrix}$
4. D.
   $\begin{pmatrix} 68 & 0 & 0 \\ 0 & 68 & 0 \\ 0 & 0 & 68 \end{pmatrix}$

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