If the sum of the numbers of an integer can be divided by 3 (or 9), then the number must be divided by () or ()

If the sum of the numbers of an integer can be divided by 3 (or 9), then the number must be divided by () or ()

If the sum of the numbers of an integer can be divided by 3 (or 9), then the number must be divided by (3) or (9). First, we use three digits to prove that a three digit ABC can be written as: 100A + 10B + C, because a + B + C = 3k, so: 99A + 9b + (a + B + C) = 99A + 9b + 3K = 3 (33a + 3B + k)... The hundred of three digits is