Let's find the cofactor:
$$
C_{12} = \begin{vmatrix}
B & -1 \\
0 & 2
\end{vmatrix}
= (B)(2) - (-1)(0) = 2B
$$
Since $C_{12} = 7$, we have $2B = 7$, so $B = \frac{7}{2}$.
(c) Now, let's find the adjoint of matrix A:
$$
\text{adj}(A) =
\begin{bmatrix}
(-1)(2) -
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