x+y+z= 900
y=3*x => x= y/3
y=z-25 => z= y+25 am scris x si z in functie de y si inlocuim in relatie
y/3 + y + y+25= 900 aducem la numitor comun
y/3 + 6y/3 + 75/3 = 2700/3 acum scapam de numitor
y + 6y + 75=2700
7y=2700-75
7y=2625
y=2625:7
y=375
x=y/3=375/3=125
z=y+25=375+25=400
