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Daca a+b=5 si b+c=7atunci 2a+5b+3c este...

Răspuns :

a+b=5 / *2⇒2a+2b=10  +

b+c=7 / *3⇒3b+3c=21

                    _________

                   2a+5b+3c =10+21=31