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calculati 7a+9b+9c+7d,stiind ca a+b+c+d=30 si a+d=10

Răspuns :

7a+9b+9c+7d,stiind ca a+b+c+d=30 si a+d=10 => b+c=20
7a+7d+9b+9c=
7(a+d)+9(b+c)=
7*10+9*20 = 
70+180=250