Explanation:

- Town A:

- Difference between males and females: 15,000

- Ratio of males to females: 7:13

- Let males be 7x and females be 13x.

- So, 13x - 7x = 15,000, which gives x = 2,500.

- Males in A: 7 * 2,500 = 17,500

- Town B:

- Difference between males and females: 20,000

- Ratio of males to females: 6:1

- Let males be 6y and females be y.

- So, 6y - y = 20,000, which gives y = 4,000.

- Males in B: 6 * 4,000 = 24,000

- Town C:

- Difference between males and females: 40,000

- Ratio of males to females: 11:3

- Let males be 11z and females be 3z.

- So, 11z - 3z = 40,000, which gives z = 5,000.

- Males in C: 11 * 5,000 = 55,000

- Town D:

- Given males in D = 13,000

- Average population of males in A, B, C, and D:

- Total males = 17,500 + 24,000 + 55,000 + 13,000 = 109,500

- Average = 109,500 / 4 = 27,375

- Population of females in D = 27,375

- Correct option is: Option 2, 27375