a question

This was asked to me in an interview. I am wondering how many of you know this

What is the type of the addition of an unsigned and a signed integer in C?

the other questions seem okay,
but srsly, who does (unsigned int + int) addition?
I would probably anwser that I don't know, since you shouldn't really do that, or that you should use a larger signed int type to store the results lololol.