14. Aflați mulțimile A şi B, dacă: a) AUB=(3, 4, 5), ANB=(3,5), B\A=Ø; b) AUB= (a, b, c), AB= (a, b), A\ B = {c}; c) AUB=(3, 4, 5, 6, 7), AB= (6, 7), A\B=(3, 4).​