To complete the second part you need to do the same thing you did in the first part. The only difference is that instead of having the allele frequencies given to you, you need to calculate them yourself. This is pretty straightforward since you know the all of the genotypes in the population.

So pretend that there are 100 individuals, 16 RR, 48 Rr, and 36 rr. There are 200 alleles in the population. Now all you need to do is calculate how many R and r alleles are in that population which will give you the allele frequencies for p and q. For example you get 32 R alleles from the dominant homozygotes. Work through the others in the same way to get the allele frequencies.