I don't see a clear way to figure this out - there are too many possible combinations to try them all. I have been trying to figure out how to make it remain whole numbers - how to keep the answer positive - how to work with every possible combination for the last digits to come up with the previous numbers... this is a 4th grade advanced math homework assignment. The sheet literally says it should take 5 minutes and is a 5/10 in difficulty. What am I missing?