The best way to start would be to see if you can make the hundred's values the same for both numbers. The only two repeating values are 9, therefore your number should start with 9. the next thing is to find the closest tens values. this is 6 and 7. so one number with be 96x and the other 97x. Next you will then find and insert either 4 or 1 into the numbers and find which difference between the two combinations is the smallest, either (964 - 971 or 961 - 974)