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Calculati3a+12b+4c+2d, stiind ca a+2b=20 si ca 3b+2c+d=40

Răspuns :

a+2b=20 rezulta 3a+6b=60
3b+2c+d=40 rezulta 6b+4c+2d=80
3a+6b+6b+4c+2d=80+60
3a+12b+4c+2d=140