To find the appropriate domain for the profit function \( P = 12x - 800 \), we need to consider what \( x \) represents in this context. In this case, \( x \) represents the number of hats sold.
Given that Steven orders 500 hats, the maximum number of hats he can sell is 500. Additionally, he cannot sell a negative number of hats. Thus, the valid range for \( x \) is from 0 to 500.
This can be expressed as:
\[ {0 \leq x \leq 500} \]
Therefore, the correct response is:
C \({0 \leq x \leq 500}\)