X:y=3=> x=3y
X:z=6=> z=x/6 dar x=3y deci z=3y/6
X+y+z=90
3y+y+3y/6=90
4y+3y/6=90 aducem la acelasi numitor
6×4y/6+3y/6=90
24y/6+3y/6=90
27y/6=90
y=90×6/27=>y=540/27=> y=20
acum stim y=20 si x=3y=> x=3×20=> x=60
y=20 si z= 3y/6=> z=3×20/6=> z=60/6=> z=10
