If an integer N is divisible by both 6 and 15, which of the following must N be divisible by?

✓ Correct Answer: Option C

For N to be divisible by both 6 and 15, N must be a multiple of their least common multiple (LCM). LCM(6, 15) = LCM(2*3, 3*5) = 2*3*5 = 30. Therefore, N must be divisible by 30.