请问数学:x+2y+3z=5①2x+3y+6z=9②5x+3y+9z=15③计算②-①x+y+3z=4,(1)③-①4x+y+6=10,(2)x-y=1,(3)x=y+1,(4)这部份计算对吗?敬请高手赐教好吗谢谢