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E=a+4b+5c-719,daca a+6b=2b+c,iar c=120

Răspuns :

Inlocuim in a doua ecuatie si avem: a=2b-6b+120 a=-4b+120 apoi inlocuim a-ul in E: E=-4b+120+4b+5*120-719 E=720-719=1.