The function \( C(x) = 30x \) calculates the cost of the field trip based on the number of students \( x \). Since \( x \) represents the number of students, it must be a non-negative integer (you cannot have a fraction of a student or a negative number of students).
Let's evaluate the given options:
- 4.5 - This is not a valid input because you cannot have a fraction of a student.
- 45 - This is a valid input (45 students).
- 14 34 - This appears to be two separate numbers, and neither is a valid input since it should only represent a number of students.
- 22 - This is a valid input (22 students).
- 15 - This is a valid input (15 students).
Thus, the valid inputs (domain) for the function \( C(x) = 30x \) are:
- 45
- 22
- 15