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a+3b=2b+c=20 aflati 7a+27b+3c

Răspuns :

7a+27b+3c il putem scrie asa 7a+21b+6b+3c=7(a+3b)+3(2b+c)=7x20+3x20=140+60=200
7(a+3b)+3(2b+c)=7x20+3x20=200