a) The starting population is in HW equilibrium and has an initial p(B) allele frequency of 0.7 is subject to fitness constraints. What will be the genotype frequencies of Bb individuals before and after one round of selection. 
q = 1 - p
p (BB) = 0.7

q (bb) = 0.3
Genotype frequencies of Bb before selection: 

 Bb  = 2pq = 2(0.7)(0.3) = 0.42 
 

Genotype frequencies of Bb before selection: 
Bb = 500/2800 = 0.18
 

b) the allele frequency q for small b after selection would be?
To find q²: 1300/2800 = 0.46
q = √0.46 = 0.68
q = 0.68

Step-by-step explanation

BB = 1000

Bb = 500

bb = 1300 
Total population = 2,800

Fomulas:        p + q = 1; p² + 2pq + q² = 1
where p = frequency of the BB (dominant allele); q =  frequency of the bb (recessive allele)
p² = frequency of individuals with BB homozygous (dominant) genotype
2pq = frequency of individuals with Bb heterozygous genotype
q² = frequency of individuals with bb homozygous (recessive) genotype