Answer:
Tuesday
Explanation:
If you read the dialogue, it tells us that Laura asks Juan, "Que dia es hoy", and his reply is "Hoy es martes, el 30 de enero"
If today is Juan's birthday, and today is Martes (Tuesday), Juan's birthday must be on Tuesday.
BTW i have no experience in Spanish so sorry if i am wrong. I am better at german and Math.
