(a) If $A=\left[\begin{array}{ccc}1 & 2 & -3 \\ 2 & 0 & -3 \\ 1 & 2 & 0\end{array}\right]$, then find $A^{-1}$ and hence solve the following system of equations:

$$\begin{array}{r} x+2 y-3 z=1 \\ 2 x-3 z=2 \\ x+2 y=3 \end{array}$$

OR

(b) Find the product of the matrices $\left[\begin{array}{ccc}1 & 2 & -3 \\ 2 & 3 & 2 \\ 3 & -3 & -4\end{array}\right]\left[\begin{array}{ccc}-6 & 17 & 13 \\ 14 & 5 & -8 \\ -15 & 9 & -1\end{array}\right]$ and hence solve the system of linear equations:

$$\begin{aligned} x+2 y-3 z & =4 \\ 2 x+3 y+2 z & =2 \\ 3 x-3 y-4 z & =11 \end{aligned}$$