Looking on the ones digit, B, you see that there are only two possibilities for B:
B = 2 or B = 7.
But B= 7 does not work: otherwise, an odd digit would be the "tens" digit in the sum "844", which is not the case.
So, we accept B= 2 for a while.
Then we see that A= 7 works.
So, our digits are A= 7, B= 2.
It gives us the ANSWER: = .
AB
+ AAB
----
844
A2
+ AA2
----
844
A
+ AA
---
84
72
+ 772
----
844