Răspuns:
Salutare!
a+b+c+d=120
a+b+c=70==>a+30+c=70==>a+c=40
b+c+d=90==> b+60=90==>b=30
c+d=60
a+b+c+d=120
a+c+b+d=120
40+30+d=120
70+d=120
d=50
c+d=60==>c+50=60==>c=10
a+c=40
a+10=40
==> a=30
Verificare
30+30+10+50=60+60=120
Răspuns:
a=30
b=30
c=10
d=50