Explanation:

Let's solve the problem step by step:

- Original number: 81465324

- Odd digits: 1, 5, 3 (decreased by 1: 0, 4, 2)

- Even digits: 8, 4, 6, 2, 4 (increased by 1: 9, 5, 7, 3, 5)

After applying the changes, the new sequence is: 90574235

Now identify the digits:

- 4th digit from the right: 4

- 3rd digit from the left: 5

Sum these digits: 4 + 5 = 9

- Option 1: 12

- Option 2: 10

- Option 3: 9

- Option 4: 8

- Option 5: 21

The correct answer is Option 3: 9