Question

Calculati 5a+7b+c , daca 4a+7b=840 si a+c=120

Answer 1

$5a+7b+c=a+4a+7b+c=(a+c)+(4a+7b)=120+840= \\ \\ =\boxed{960}.$

Answer 2

5a+7b+c=a+4a+7b+c=120+840=960