Răspuns :
Cred ca asa este mai usor decat cu metoda figurativa:
a+b+c=340.
a+b=b+c+80.
b=50+c
b+c+80+c=340.
50+c+c+80+c=340.
3c=340-130
3c=210
c=70
b=70+50
b=120
a=150
a+b+c=340, a+b=b+c+80. Adica a=c+80, si b=c+50 ,c /-----/, b/-----/+50, a/----/+80; inlocuim in a+b+c=340 totul in functie de c si obtinem : c+80+c+50+c=340 ,3c+130=340 , 3c=210 , c=70 , a=c+80= 70+80=150 ,b=c+50= 70+50=120 verificare :150+120+70=340