Explanation:

- Start with the given averages:

- The total of the 18 numbers is 18 × 52 = 936.

- The sum of the first 8 numbers is 8 × 62 = 496.

- The sum of the next 7 numbers is 7 × 45 = 315.

- Find the sum of the last three numbers (16th, 17th, 18th):

- Total of the first 15 numbers: 496 + 315 = 811.

- Sum of the last three: 936 - 811 = 125.

- Express the relationships among the last three numbers:

- 16th number = 17th number - 6

- 17th number = 18th number + 1

- Let the 18th number be x:

- So, the 17th number is x + 1.

- The 16th number is x - 5.

- Sum of 16th, 17th, 18th numbers: (x - 5) + (x + 1) + x = 125.

- Solve:

- 3x - 4 = 125

- 3x = 129

- x = 43

- Find the average of the 16th and 18th numbers:

- 16th number: 43 - 5 = 38.

- 18th number: 43.

- Average: (38 + 43) / 2 = 40.5.

Option 2, 40.5 is correct.