Here, in units place,

A + A +A = A

Ie. 3A = A, ie. 3 = 1 which is wrong.

Hence A is greater than 10, where, 1 carry is given to tens place.

∴ A + A + A = A + 10

∴ 3A = A + 10

∴ 2A = 10

∴ A = 5

Now, in tens place,

B = 1 … as 1 is carried