We have,

$|A|=2(-1-0)-1(4-0)+3(8-7)$

$=2(-1)-1(4)+3(1)$

$=-2-4+3$

$=-3$

Now, $A_{11}=-1-0=-1, A_{12}=-(4-0)=-4, A_{13}=8-7=1$

$A_{22}=-(1-6)=5, A_{22}=2+21=23, A_{23}=-(4+7)=-11$

$A_{31}=0+3=3, A_{22}=-(0-12)=12, A_{33}=-2-4=-6$

$\therefore a d j A=\left[\begin{array}{ccc}-1 & 5 & 3 \\ -4 & 23 & 12 \\ 1 & -11 & -6\end{array}\right]$

$\therefore A^{-1}=\frac{1}{|A|} a d j A=-\frac{1}{3}\left[\begin{array}{ccc}-1 & 5 & 3 \\ -4 & 23 & 12 \\ 1 & -11 & -6\end{array}\right]$