I need help with this Hardy Weinberg problem?

Which is dominant, if any?

The Hardy-Weinberg equation is p + q = 1 where the total frequency of two alleles for a single gene in a population is 1 (there are only two alleles, so the sum of the frequencies has to add up to 100%).  Let's assume that the white cats are a result of the recessive allele and that white only results from the homozygous condition.   Then, we let the frequency of that allele be represented by q, so the black allele frequency is represented by p.  So, the population size is 100 and 20 of the population are white cats.  Thus, 20/100 = 0.2 = the frequency of homozygous recessives = q^2:

q^2 = 0.2
q = 0.4472

Therefore, since p + q = 1, then p = 1 - q = 1 - 0.4472 = 0.5528

So, the frequency of the black allele is 0.5528 and the frequency of the white allele is 0.4472

Note that it doesn't matter which allele is designated as the recessive allele, we could have designated the black allele as the recessive and the white allele as dominant and the math would be the same, just that the frequency of the black allele (if we had said it was recessive) would be 0.4472 and the frequency of the white allele (if we had said it was dominant would be 0.5528