a/b =3/7 si 2a+5b= 82 (din prima scoatem a in functie de b) => a=3b/7
inlocuim a in cea de-a doua ecuatie 2*3b/7+5b=82 (aducem membrul stang la acelasi numitor) =>6b/7+ 35b/7=82 =>41b/7=82 => b=82*7 / 41=> b=574/41 =>b=14
(inlocuim in prima) a/14=3/7 =>7a= 14*3 => a= 42/7 => a=6
