Explanation:

- Let's examine the sequence: 9, 5, 6, 10.5, 23, 61, 18.

- Start with 9, the difference to 5 is -4.

- From 5 to 6, the increase is 1.

- From 6 to 10.5, the increase is 4.5.

- From 10.5 to 23, the increase is 12.5.

- From 23 to 61, the increase is 38.

- From 61 to 18, there is a decrease of 43.

- The sequence doesn't follow a recognizable pattern due to inconsistent differences.

- Given these differences, "61" doesn't fit logically in the progression.

- Therefore, Option 1 - 61 is the inconsistency here.