A+B+C=853
a+b=560
b+c=427
------------------------
? a,b,c
Inlocuim mai intai
stim ca a+b+c=853
560+c=853
c=853-560
c=293
stim ca b+c=427
b+293=427
b=427-293
b=134
a+b+c=853
inlocuim ce am aflat
a+134+293=853
a+427=853
a=853-427
a=426
proba 426+134+293=853
