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Afla 7a+9b+9c+7d dacă a+B+c+d=30 si a +d=10

Răspuns :

7a+7b+7c+7d=30*7
=210
7a+7d=70
210-70=140=7b+7c
b+c=140:7=20
7a+9b+9c+7d=7*10+9*20=70+180=250