The expression "12C" is often interpreted as a combination notation, commonly denoted as $\binom{n}{r}$, where $n$ is the total number of items, and $r$ is the number of items to be chosen. However, it seems like the value for $r$ is missing.

To clarify, if you're referring to a combination, the full notation should look like this: $\binom{12}{r}$. You would need to specify the value of $r$ to calculate the combination.

For example, if you meant $\binom{12}{3}$, this would be calculated as:

$\binom{12}{3} = \frac{12!}{3!(12-3)!} = \frac{12 \times 11 \times 10}{3 \times 2 \times 1} = 220$

Please provide the value of $r$ if you want to calculate a specific combination.

Would you like more details on combinations or have any other questions?

Here are some related questions:

1. What is the formula for calculating combinations?
2. How do combinations differ from permutations?
3. Can combinations be used in probability problems?
4. What are some real-life applications of combinations?
5. How do you compute combinations with large numbers?

Tip: When dealing with combinations, remember that order does not matter, unlike permutations where the sequence is important.