[tex]B)\begin{bmatrix}a & b \\ c & d \\ \end{bmatrix}=\frac{1}{|A|}\cdot\begin{bmatrix}d & -b \\ -c & a \\ \end{bmatrix}[/tex]
1) Let's start out with that writing the rule to get a Matrix 2x2:
One over the determinant of this very Matrix times the original matrix with swapped entries on the main diagonal, and with swapped and opposite entries on the second diagonal:
[tex]\begin{bmatrix}a & b \\ c & d \\ \end{bmatrix}=\frac{1}{|A|}\cdot\begin{bmatrix}d & -b \\ -c & a \\ \end{bmatrix}[/tex]
Note that |A| is the notation for the determinant of A
2) Thus this is the answer.
