Suppose a population is carrying a condition controlled by two alleles: p (dominant) and p (recessive). only homozygous individuals that have two copies of the recessive allele have the condition. if the p allele is found in 15 percent of the population, what's the frequency of the pp genotype?

If we know that we have Pp PP and pp individuals.

Only homozygous individuals that have two coies of the recessive allele have the conditions - 15%
If we know that the p allele itself is found in 15% of the population. 

We know that the P allele is found in 75% of the population (100 - 15)

To now know what is the frequency of the PP genotype, we can calculate this using simple mathematics:

If P is now 75%, to get 2x P we have to calculate 75%*75% =56.25%

So an individual who is of the genotype PP can be most likely found with the frequency of around 60% in this population.