3-and-1 doesn't really answer the question, which is related to what is the basic spot in these kinds of plays. Rule 10-2-2 is the rule you want to read but to recap it, the basic spot is (when there's no change of team possession during the down):
Running plays where the related run ends behind the NZ: previous spot
Running plays where the related run ends beyond the NZ (or there is no NZ): end of the related run
Legal forward pass plays: previous spot
Legal kick plays: previous spot or the postscrimmage kick spot