To calculate the average number of female athletes from Country B, we need to divide the total number of participants by the number of years.
Based on the provided data for female athletes from Country B, the total number of participants across all years is calculated, and then we divide by the total number of years to get the average.
For example, if the sum of female participants across all years is 6000 and there are 10 years considered, the average is:
\[
\text{Average} = \frac{6000}{10} = 600
\]
Thus, the correct answer is (3) 600.