A 1
+ 1 B
______
B 0
∵ 10 - 1 = 9
∴ B = 9
Also 9 - 1 = 8 - 1 = 7
∴ ______
A = 7
We have 7 1
+ 9 1
______
9 0 _
Thus, A = 7 and B = 9