9000019910

The augmented matrix of a system of three equations with three unknowns is row equivalent to the following matrix $A^{\prime }$. Find the solution of the system. $$A^{\prime }=\left(\begin{array}{cccc}-1& -6& 1& -20\\ 0& 5& 4& -12\\ 0& 0& 0& -8\end{array}\right)$$