Formal:
* तुम्ही कुठे आहात? (Tumhi kuthe ahat?)
Informal:
* तू कुठे आहेस? (Tu kuthe ahes?)
Explanation:
* तुम्ही (Tumhi) means "you" (plural, formal)
* तू (Tu) means "you" (singular, informal)
* कुठे (Kuthe) means "where"
* आहात (Ahat) means "are" (plural, formal)
* आहेस (Ahes) means "are" (singular, informal)
You would use the formal phrase when talking to someone older, in a professional setting, or someone you don't know well. The informal phrase is used with friends, family, or someone you're comfortable with.