$9\mathrm{.}3($a$)$ Write each system of equations as an augmented matrix, $($b$)$ find the solutions using Gaussian

elimination and back substitution, $($c$)$ then check the solution using MatLab commands: $\frac{\frac{?}{?}}{?}$ and inv.

$x_1+2x_2-3x_3+x_4=-1$

$x_2-2x_3+x_4=2$

$x_1,+x_3-x_4=1$

Turn in the MatLab output.