When the number of individuals are already mentioned derive the frequency in 100 individuals: for this question which will be as following --
Number of homozygous dominant 49% (
Number of heterozygous dominant 42% (
Number of homozygous recessive 9% (
(There are two alleles B and b)
Now you can derive the frequency of alleles:
Frequency of allele B =
Frequency of allele b =
(According to Hardy Weinberg principle --
sum of all the frequencies of alleles = 1
in this case .7 + .3 = 1 )