a+b+c=56 ; a:b= cat 2 rest 7 ; a=2b+7 (teorema impartirii cu rest)
b:c= cat 3 rest 3 ; b=3c+3 ; 3c=b-3 ; c = (b-3)/3, inlocuim a si c in suma
2b+7+b+(b-3)/3=56 ; numitor comun 3
6b+21+3b+b-3 = 168 ; 10b = 168-21+3 = 150 ; b=150/10 = 15 ;
a=2*15+7 = 37 ; c=(15-3)/3 = 12/3 = 4