Explanation:

- The average of five numbers is 7, so their total sum is 5 * 7 = 35.

- Adding three new numbers leads to eight numbers with an average of 8.5.

- The total sum for these eight numbers is 8 * 8.5 = 68.

- The increase from 35 to 68 is due to the three new numbers, which sum up to 68 - 35 = 33.

- The average of the three new numbers is 33 / 3 = 11.

- Option 3: 11 is the correct answer.