156920

If you look, the 1st and 3rd digit cannot be the same, so the smaller number will have a larger 1s digit. You have to borrow. (998 reverse is 899. As you can see 998 has a smaller 1s digit than 899). The difference between the numbers is 099. Reverse is 990. The middle digit is 9. That means the 10 s digit is always 18. Carry that 10 over to the 100s. You will notice, using the 10 you carried over, the answer will be 10. So far, our number is 1080. The 1s digits of the numbers you are adding will total to 9 so the 1s is 9. The answer to any 3 digit number where the 1st and 3rd digits are not the same, using this method, will be 1089.