The addition of A and B is giving 9 i.e., a number whose ones digits is 9. The sum can be 9 only as the sum of two single digit numbers cannot be 19. Therefore, there will not be any carry in this step.
In the next step, 2 + A = 0
It is possible only when A = 8
2 + 8 = 10 and 1 will be the carry for the next step.
1 + 1 + 6 = A
Clearly, A is 8. We know that the addition of A and B is giving 9. As A is 8, therefore, B is 1.
Therefore, the addition is as follows.
128 + 681 = 809
Hence, the values of A and B are 8 and 1 respectively.