A dihybrid genetic question...?

First you know that both flowers are red, lets call the gene for it R, there is another color in the offspring, white, lets call it r. There are more red flowers than white flowers so you can safely say that red is dominant over white. Now since there was both red and white flower offspring you now that each of the adult flowers are heterozygous, meaning one of each gene. This is because in order to have white, you need a genotype of r,r. This is because in order for a recessive to be expressed you need both recessive copies of the gene. So both parents must be R,r. If you do the punnit square you will see that 1/4 of the offspring have r,r. Which is what you needed. Hope that helped.