156283

First we quickly found out that there were 2 answers for the first question.
The first one was the number 321 and the other number was 123.

The second question was a bit tricky because now there were 4 digits instead of 3 digits. We started to guess and check. we figured that this would be the easiest way to solve the problem. An easy way to recognise multiples of 3 is if the digit sum is a multiple of 3. A way to recognise multiples of 4 is if the end digit/s are multiples of 4. The quickest way to find multiples of 5 is if the number ends in 5 or 0.