Would you use "tu" or "vous" with the following person?

In French, "tu" is used for informal or familiar situations, typically with friends, family, or people of the same age. "Vous" is used for formal situations, or when addressing someone you don't know well, such as in a professional context or with someone older.

If you are on familiar terms with Marc, you would use "tu." If you don't know him well or want to be formal, you would use "vous."

Since no context is provided, it's difficult to give a definitive answer. However, in typical situations, one might lean towards using "tu" with someone named Marc if they are of similar age or friendly. If unsure or if the setting is formal, "vous" would be the safer choice.