Löse das lineare Gleichungssystem.


`{(-15x,+,5y,+,9z,-,5w,=,-20),(-3x,+,3y,+,3z,-,w,=,6),(3x,-,y,-,3z,+,w,=,4),(30x,-,10y,-,18z,+,7w,=,40):}`

x =  
y =  
z =  
w =