The answer is Rr and rr.
R - dominant allele for red eyes
r - recessive allele for sepia eyes
If a red-eyed heterozygous fly Rr mates with a sepia-eyed homozygous fly rr, the possible genotypes of the offspring are Rr (heterozygotes) and rr (recessive homozygotes).
Parents: Rr x rr
Offspring: Rr Rr rr rr
Thus, half of the offspring will have genotype RR and will have red eyes while half of the offspring will have genotype rr and will have sepia eyes.