Răspunsuri

2014-10-12T17:24:04+03:00
A+b=20|*3
3a+3b=60 (1)
b+c=30|*4
4b+4c=120 (2)

Adunand relatiile (1) si (2):
3a+3b=60
4b+4c=120
obtinem 3a+7b+4c=60+120=180