Answer: 48%
Because the population is in hardy-weinberg equilibrium, that means the sum of m and n alleles frequency would be 1
If m is 0.4, then n would be:
m+n=1
0.4+n=1
n=0.6
The frequency of organism with heterozygote genotype would be:
2 * m* n= 2 * 0.4 *0.6=0.48=48%