If the sum of the digits of a given number equals nine or a multiple of nine, nine is a factor of that number.
If that is the case, then three is a factor of the original number.
12
No number satisfies all of those conditions.
12
No factor of 9 has three digits. 450 is a three-digit multiple of 150 (and of 9) with a digit sum of 9.
No. To find if a number is a factor of 3, add the number's digits. If the resulting number is a multiple of 3, then the original number is a multiple of 3. In 4339, the digits of the number added together is 19, which is not a multiple of 3.
450 or 900
If the last two digits of your target number are a multiple of 4, 4 is a factor of the whole number.
Add up the digits of the given number. If they total a multiple of three, the number has three as a factor.
21 or 35
The number is 35.