A post apocalypse puzzle

A little puzzle:

We are in a post apocalypse-age and want to enter a town.

To do so we have to solve a little puzzle. All people in the town know how to solve the puzzle, but we not, because we are not from the town and we don´t like to ask any inhabitants, because we don´t want that the inhabitants know that we are not from their town.

We are watching the guard of the town and how the people enter the town. The guard asks every person a question which the people has to answer to enter town, like: I say 84, what do you say? Answer: 11. Or I say 9, what do you say: 6. Or I say 1122, what do you say: 14 ...

After a while we think that we understood the puzzle and are ready to enter the city. We step to the guard, who asks: I say 63, what do you say?

So what do we say?