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Buna ma poate  ajuta cineva la problema.Calculati 3a+5b+2c stiindca a+b=5 si b+c=7


Răspuns :

3a+5b+2c=?
a+b=5,b+c=7
a=5-b,c=7-b
3(5-b)+5b+2(7-b)=15-3b+5b+14-2b=29