Number Series:
The given number series is 9, 12, 10, ?, 12, 21, 15, 27. We need to find the missing term in the series.

Observations:
To find the missing term, let's analyze the given series:
- The first term is 9.
- The second term is obtained by adding 3 to the previous term: 9 + 3 = 12.
- The third term is obtained by subtracting 2 from the previous term: 12 - 2 = 10.
- The fourth term is missing.
- The fifth term is obtained by adding 2 to the previous term: 10 + 2 = 12.
- The sixth term is obtained by adding 9 to the previous term: 12 + 9 = 21.
- The seventh term is obtained by subtracting 6 from the previous term: 21 - 6 = 15.
- The eighth term is obtained by adding 12 to the previous term: 15 + 12 = 27.

Pattern Analysis:
From the observations, we can identify the following patterns in the series:
- The series alternates between adding and subtracting a specific number.
- The number being added or subtracted is changing with each term.
- The number being added or subtracted is increasing by a fixed amount with each term.

Pattern Identification:
Let's analyze the changes in the number being added or subtracted:
- The first change is from 3 to -2 (decreasing by 5).
- The second change is from -2 to 2 (increasing by 4).
- The third change is from 2 to 9 (increasing by 7).
- The fourth change is from 9 to -6 (decreasing by 15).

Missing Term:
To find the missing term, we need to continue the pattern:
- The fifth change should be an increase of 22 (15 + 7).
- The sixth change should be a decrease of 37 (22 - 15).
- The seventh change should be an increase of 59 (37 + 22).

Let's apply these changes to the last term in the series (27):
27 + 22 = 49 (missing term)

Conclusion:
The missing term in the given number series is 49. Therefore, the correct answer is option B) 49.