Răspuns:
a+b = 13
2xb+c=15
2a+8b+3c=?
-------------------
a+b =13 / x2
2a+2b=26
2b+c=15 /x3
6b+3c=45
2a+2b+6b+3c=26+45
2a+8b+3c=71
