If you have an airplane with 50 seats and only 14 pax on board how many flight attendants do you need?

This is the part 91 reg I found:

http://www.risingup.com/fars/info/part91-533-FAR.shtml

I'm sure its different for Part 121? Whats the reg number? Trying to prepare for an interview and this was a Grey area... thanks.