Explanation:

- Let's decipher the series: 19, 38, 35, ?, 135, 810.

- The pattern isn't readily apparent, so let's look closer.

- First to second number (19 to 38): Increase by 19.

- Second to third number (38 to 35): Decrease by 3.

- Then, we have a missing number before reaching 135.

- Third to fifth number: Seems to involve a more significant change.

- Exploring differences: Check simple arithmetic or multiplicative operations.

- Seems like alternating between adding and subtracting:

- After 35, add another sequence.

- For example, evaluate doubling or other shifts to reach 135.

- Next, calculate possible numbers fitting the series.

- Given choices help test possibility: 146, 142, 137, 140.

- Correct Answer: Option 4 - 140