Solution (source code)

= Solution

For $\lambda=1$ and $\mu=1/2$, the third equation gives $x=z-1$. Combining it with $2x-z=-4$ gives $z=-2$ and $x=-3$, after which the second equation gives $y=12$. Hence
$$
\boxed{(x,y,z)=(-3,12,-2).}
$$
The <coefficient matrix> has <determinant> $\lambda-2=-1\ne0$, proving uniqueness. Direct substitution gives the required right-hand sides $1$, $5$ and $-1$.