3x Rule

[Rhonda Burnette]

 Me and my friends are trying to get a place to rent and we have found this wonderful duplex that's $1159. The agent told us that since me and one of my roommates are full time students that we only have to provide an school schedule but my other roommate is not a student an has to prove that he makes 3x the rent. 

This is where I get confused, why is just him that has to make 3x? He makes 16hr at 40hrs a week an still doesn't make 3x the rent by himself. I was thinking it was because he worked full time but I also work full time while being a full time student. Please help me figure this out I am so confused.