Upon inspection, it appears that the sequence consists of two interleaved patterns.
If we separate the sequence into the two patterns, it becomes:
Pattern 1: 6, 7, 8, ... Pattern 2: 12, 11, 10, ...
In Pattern 1, each term increases by 1.
In Pattern 2, each term decreases by 1.
Hence, we can continue the sequence as follows:
Pattern 1: 6, 7, 8, 9, ... Pattern 2: 12, 11, 10, 9, ...
The next term in the sequence would be the next term in Pattern 1, which is 9.
Therefore, the missing number in the sequence is 9.
Pattern 1: 6, 7, 8, ... Pattern 2: 12, 11, 10, ...
In Pattern 1, each term increases by 1.
In Pattern 2, each term decreases by 1.
Hence, we can continue the sequence as follows:
Pattern 1: 6, 7, 8, 9, ... Pattern 2: 12, 11, 10, 9, ...
The next term in the sequence would be the next term in Pattern 1, which is 9.
Therefore, the missing number in the sequence is 9.