x=numarul de castane stranse de Dragos
y=numarul de castane stranse de Robert
z=numarul de castane stranse de Petru
x+y+z=380 castane
x+y=236 castane
z=x+36
236+z=380
z=380-236
z=144 castane a strans Petru
x+36=144
x=144-36
x=108 castane a strans Dragos
108+y=236
y=236-108
y=128 castane a strans Robert