1) x+y+z = 54
2) y+3=2x
3) z=x+y
=> din 1) si 3) obtinem
1) x+y+z = 54
3) z=x+y
--------------------
z+z = 54 => 2z=54 => z = 27
3) z=x+y => x+y = 27
2) y+3=2x => y+3-2x=0
-----------------------------------
2y+3 = 27 => y = 12
=> din 3 avem ca
27 = x + 12 => x = 15
verificam
x+y+z = 54... ???
15+12+27 = 54.. DA