When a positive integer x is divided by 7, the remainder is 4. What is the remainder when 3x is divided by 7?

✓ Correct Answer: Option D

If x = 7k + 4 for some integer k, then 3x = 3(7k + 4) = 21k + 12. Since 21k is divisible by 7, the remainder of 3x divided by 7 is the same as the remainder of 12 divided by 7, which is 5.