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a+3b=50
2b+5c=80
Calculați: 2a+12b+15c


Răspuns :

A+3b=50
2b+5c=80
2a+12b+15c=?
____________
2×(a+3b)=50×2=100=2a+6b
3×(2b+5c)=80×3=240=5b+15c
2a+12b+15c= 100+240=340