Jobs.... they do different jobs.
Nice because : Biotic potential is the ability of a population of living species to increase under ideal environmental conditions – sufficient food supply, no predators, and a lack of disease. An organism’s rate of reproduction and the size of each litter are the primary determining factors for biotic potential.
Here, given-
homozygous alleles 'a' have a frequency of 0.3.
Also the alleles are in equilibrium in a Hardy-Weinberg population. The frequency of individuals that are homozygous for this allele are= 0.49.
The Hardy-Weinberg equilibrium can be defined as the principle which states that the variation in the genetic makeup of a population remains constant and unchanged till there are no external interferences, influencing the population.
Calculation-

Then to find the frequency of the individuals homozygous for this allele the following formula needs to be used-


Thus, the individuals homozygous for the allele can be calculated by 
Learn more about the Hardy-Weinberg equilibrium here-
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