a+b+c=1080
a=2b
a=c/3 ; c=3a ; c=3*2b ; c =6b ; inlocuim pe a si c in prima relatie
2b+ b+6b=1080
9b =1080
b=120
a=2b
a=2*120 =240
c=6b
c=6*120 =720
verif ; 240+120+720 =1080
2)x+y+z=200
z/2=y/3 =x/5
z+y+x/2+3+5 =200/10 =20
z /2 =20 ; z =2*20 =40
y/3 =20 ; y =3*20 =60
x/5 =20 ; x =5*20 =100
verif ;100+60+40 =200
3) 200:5 =40 lei /m
7*40 =280 lei