In order to answer this, you will need to set up a Punett Square (I have attached a picture).
Since Rr is the genotype of round seeds, we know that round must be dominant to wrinkled, and therefore represented by the allele, R.
Since rr is the genotype of wrinkled seeds, we know that wrinkled must be the recessive trait, and there represented by the allele, r.
Since the Punnett Square shows that the genotype ratio is 2Rr : 2rr, or simplified, 1Rr : 1rr, we now know that there is a 50% chance the offspring will have wrinkled seeds.
Since Rr is the genotype of round seeds, we know that round must be dominant to wrinkled, and therefore represented by the allele, R.
Since rr is the genotype of wrinkled seeds, we know that wrinkled must be the recessive trait, and there represented by the allele, r.
Since the Punnett Square shows that the genotype ratio is 2Rr : 2rr, or simplified, 1Rr : 1rr, we now know that there is a 50% chance the offspring will have wrinkled seeds.