To have the disease, males need only one copy of the affected X.
So, the frequency of affected males will be the frequency of the disease allele = 0.02
Females must inherit two copies and be homozygotes, so the frequency of affected females will be the double of frequency of the disease allele = (0.02)
Since the ratio between female and male is 50:50 that is half of the population is male and half female
Then the overall frequency of the disease will be,
(0.5) (0.02) + (0.5) (0.0004) = 0.01 + 0.0002
Thus, the frequency of affected individuals in this population is 0.0102.