Step 1: There are 12 vacancies to be filled, and 3 of these vacancies are reserved for candidates from the scheduled caste.
- The number of ways to select 3 candidates from the 5 scheduled caste candidates is \( 5C3 \).
- After selecting the 3 scheduled caste candidates, 9 vacancies remain, and they can be filled by any of the remaining 22 candidates. The number of ways to select 9 candidates from the 22 is \( 22C9 \).
Step 2: Therefore, the total number of ways to fill the vacancies is:
\[
5C3 \times 22C9.
\]