A population of horses has individuals that are either gray or chestnut colored. The gray color allele, G, is dominant over the chestnut color allele, g. If the frequency of the gray allele in the population is 0.8, what percent of horses are gray? 64 percent 96 percent 32 percent 80 percent

It's not really a Punnet square question - it's a Hardy-Weinberg population genetics problem.

If the frequency of the gray allele = 0.8, then the frequency of the chestnut allele = 0.2.

Then, frequency of genotype GG = p-squared = 0.8 x 0.8 = 0.64

and frequency of genotype Gg = 2 x pq = 2 x 0.8 x 0.2 = 0.32

So, the proportion of gray horses = 0.64 + 0.32 = 0.96, or 96%

[Alternatively, you can just say chestnuts = q-squared = 0.2 x 0.2 = 0.04 or 4%. So - grays = 100-4 = 96%]