If mothers blood group is rhs o neg and baby blood group is o positive what would the fathers blood group be?

Father's blood type: Father is O positive. In the A-B-O nomenclature, A and B and dominant and Rh + is dominant over Rh -. That means that the baby had to get an O allele from both mother and father and at least one Rh + allele from a parent. Mom is OO neg neg and that means that the father has to be OO pos neg or OO pos pos. Either way, the father is phenotypically O pos.