Explanation:

- The average of eleven numbers is 80, so the total sum of these numbers is 11 * 80 = 880.

- The average of the first four numbers is 74.5, leading to a total sum of 4 * 74.5 = 298.

- The average of the next four numbers is 82.5, summing to 4 * 82.5 = 330.

- For the last three numbers, their total sum is 880 - (298 + 330) = 252.

- Let the tenth number be x. Then, the ninth is x + 6, and the eleventh is x + 6.

- Thus, for the last three numbers: (x + 6) + x + (x + 6) = 252, simplifying to 3x + 12 = 252.

- Solving gives: 3x = 240, so x = 80.

- Therefore, the ninth number is 86, and the eleventh is 86.

- The average of the ninth and eleventh numbers is (86 + 86) / 2 = 86.

Correct Answer: Option 3 - 86