Answer:
42 and 39
Explanation:
The best method in my opinion is to guess and check. So, you would start off by dividing 1638 by any number you see fit (I started with 34), and keep increasing or decreasing until you get whole numbers that are three integers apart. I understand that this is a little tedious but I'm not aware of a better solution as of right now, so that's the best that I've got! Please let me know if you need more help and I will be happy to help!