Answer:
Bien, ¡gracias! ¿Y tú?
Step-by-step explanation:
In Spanish there are some basic phrases for peer communication. As for example, it can be: "¡Hola! ¿cómo estás?" or "¿Cómo va tu día?" Although the first one can be applied to almost all types of cases, the question referred to how the day of the person you are talking with goes is not recommended to use it if there is no previous trust. To answer, you can use: "Estoy bien. ¡Gracias!" in case you are well, or else "No estoy muy bien. Gracias por preguntar." In case it is not so.