for this you would use a punnet square (ill try my best to show it while typing)
heterozygous means different, so with the purple flower youd get the gene shown as Pp and put it into the punnet square
P p
P PP Pp
p Pp pp
given the possibilities in the punnet square the genes with at least one P is going to be purple and the genes with 2 "p"s are going to be white
so you would have
25% Dominate Homozygous Purple
50% Dominate Heterozygous Purple
25% Recessive Homozygous White
