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calculati 2a+5b+3c stiind ca a+b=20 si b+c=30


Răspuns :

a+b=20 | *2
b+c=30 | *3

2a+2b=40
3b+3c=90
Le adunam

2a+2b+3b+3c=40+90
2a+5b+3c=130