The factors of 75 are the numbers that can divide 75 without leaving a remainder. The prime factorization of 75 is \( 3 \times 5^2 \).
Among the choices provided:
- 6: Not a factor (75 ÷ 6 = 12.5)
- 9: Not a factor (75 ÷ 9 = 8.33)
- 3: Is a factor (75 ÷ 3 = 25)
- 4: Not a factor (75 ÷ 4 = 18.75)
Therefore, the number that is a factor of 75 is 3.