1. 2n=(n/2)+27, numitor comun 2 ; 4n=n+54 ; 3n=54 ; n=54/3 = 18
2. a+b+c=30 ; a-3=b =c+3 ; a=b+3 ; c=b-3 ; inlocuim a si c in prima relatie
b+3+b+b-3=30 ; 3b=30 ; b=30/3 = 10 portocale in a doua cutie
a=10+3=13 portocale in prima cutie ; c=10-3 = 7 portocale in a treia cutie