These phrases mean the same question adressed to the someone who just asked you. So, you choose the same preposition (or no prepositions) before the pronoun as it was in first question, and the same case of pronoun. Generally, "вас" is accusative case, "у вас" is genitive case. Examples: 1) Как [вас] зовут? - А вас? (no prep.) What is your name? - And yours? 2) Кто [вас] сюда позвал? - А вас? (no prep.) Who invited you here? - And you? 3) Как [у вас] дела? - А у вас? (prep.) How are you? - And you? 4) Кто [у вас] преподает русский? - А у вас? (prep.) Who is your russian teacher? - And yours? The same rule works for other pronouns, cases and prepositions.

А Вы: - Я люблю кофе, а Вы? - Я учу английский и китайский, а Вы? - Я умею водить машину, а Вы нет. А Вас: - Меня зовут Иван, а Вас? - Меня пригласили на вечеринку, а Вас? - Я знаю Вашего мужа, а Вас нет. А у Вас: - У меня всё хорошо, а у Вас? - У меня есть машина, а у Вас? - У меня есть кошка, а у Вас нет.

I'll give examples. Меня зовут Михаил. А вас? ( my name is Michael. And yours? ) У меня есть немного времени. А у вас? (I have a little free time. And what about you? )

Привет Velvet! Меня зовут Alexandr, мы можем попробовать поговорить с тобой. Мне интересно знакомиться с людьми из разных стран! Мне это понравилось, когда я первый раз путешествовал:) Let's talk!

hello, I write on behalf of my wife who is registered on Italki but never uses this site because she does not like it. She is Russian and she is studying English alone with a course, but she needs to practice and make friends too. She is a 3D graphic modeller and we want to go abroad, so we study languages. I'm not good in English even though I understand, I'm studying German right now. She always uses Skype for work and so she always uses it and can chat or talk in her spare time, she is looking for women because we have noticed that men usually think of flirting and we do not like it. I'll put the link of her profile if you want to do language exchange .. she is nice, good and quiet. Her profile (she is also among my friends here) https://www.italki.com/user/3654037 bye!!!!