In the context of Henry's t-shirt printing business, the variable \( x \) represents the number of shirts sold. Since Henry ordered 600 shirts, the maximum number of shirts he can sell is 600. He cannot sell a negative number of shirts, and therefore the minimum number of shirts he can sell is 0.
Thus, the domain for this profit function is defined by the condition that \( x \) must be between 0 and 600, inclusive.
Therefore, the correct answer is:
B {0 ≤ x ≤ 600}