Lineare Gleichungssysteme mit 3 Unbekannten (8. Klasse)

Löse die folgenden Gleichungssysteme mit einem Verfahren deiner Wahl:

1. $$\begin{array}[t]{rcrcrcrcr}-3\,x & \hspace{-0.7em}- & \hspace{-0.7em} \,\,y & \hspace{-0.7em} - & \hspace{-0.7em} 7\,z & \hspace{-0.7em} = & \hspace{-0.7em} -40\\ -6\,x & \hspace{-0.7em} + & \hspace{-0.7em} 5\,y & \hspace{-0.7em} + & \hspace{-0.7em} 6\,z & \hspace{-0.7em} = & \hspace{-0.7em} 18\\ -2\,x & \hspace{-0.7em} - & \hspace{-0.7em} 5\,y & \hspace{-0.7em} + & \hspace{-0.7em} 4\,z & \hspace{-0.7em} = & \hspace{-0.7em} 60\end{array}$$
2. $$\begin{array}[t]{rcrcrcrcr}-3\,x& \hspace{-0.7em} & \hspace{-0.7em} & \hspace{-0.7em} + & \hspace{-0.7em} 7\,z & \hspace{-0.7em} = & \hspace{-0.7em} -23\\ -7\,x & \hspace{-0.7em} - & \hspace{-0.7em} 5\,y & \hspace{-0.7em} + & \hspace{-0.7em} \,\,z & \hspace{-0.7em} = & \hspace{-0.7em} 8\\ 3\,x & \hspace{-0.7em} - & \hspace{-0.7em} 7\,y& \hspace{-0.7em} & \hspace{-0.7em} & \hspace{-0.7em} = & \hspace{-0.7em} -33\end{array}$$
3. $$\begin{array}[t]{rcrcrcrcr}-5\,x & \hspace{-0.7em} + & \hspace{-0.7em} \,\,y & \hspace{-0.7em} + & \hspace{-0.7em} 7\,z & \hspace{-0.7em} = & \hspace{-0.7em} 51\\ -3\,x & \hspace{-0.7em} - & \hspace{-0.7em} 5\,y & \hspace{-0.7em} + & \hspace{-0.7em} 6\,z & \hspace{-0.7em} = & \hspace{-0.7em} 60\\ & \hspace{-0.7em} & \hspace{-0.7em} \,y& \hspace{-0.7em} & \hspace{-0.7em} & \hspace{-0.7em} = & \hspace{-0.7em} -3\end{array}$$
4. $$\begin{array}[t]{rcrcrcrcr}6\,x & \hspace{-0.7em} - & \hspace{-0.7em} 5\,y & \hspace{-0.7em} - & \hspace{-0.7em} 2\,z & \hspace{-0.7em} = & \hspace{-0.7em} -61\\ -4\,x & \hspace{-0.7em} - & \hspace{-0.7em} 5\,y & \hspace{-0.7em} - & \hspace{-0.7em} 7\,z & \hspace{-0.7em} = & \hspace{-0.7em} -1\\ -2\,x & \hspace{-0.7em} - & \hspace{-0.7em} 2\,y & \hspace{-0.7em} - & \hspace{-0.7em} 2\,z & \hspace{-0.7em} = & \hspace{-0.7em} 0\end{array}$$