Formal:
* "Bien, gracias, ¿y usted?" (This is the most formal and polite way to say it.)
Informal:
* "Bien, gracias, ¿y tú?" (This is the most common way to say it with friends or family.)
* "Estoy bien, gracias, ¿y tú?" (This is a slightly more literal translation, but still informal.)
Even More Casual:
* "Todo bien, gracias, ¿y tú?" (This is a very informal way to say it, and is more appropriate with close friends.)
Important Note: The question "and you?" is optional. You can simply say "Bien, gracias" (I'm good, thanks) and the other person will understand that you are inquiring about their well-being.