For unit’s place,

We have two conditions, when 7 + B ≤ 9 and 7 + B > 9

For 7 + B ≤ 9

7 + B = A

∴ A – B = 7 …(1)

In ten’ place,

B + A = 8 …(2)

Solving 1 and 2 simultaneously,

2A = 15 which means A = 7.5 which is not possible

Hence, our condition 7 + B ≤ 9 is wrong.

∴ 7 + B > 9 is correct condition

Hence, carrying one in ten’s place and subtracting 10 from unit’s place,

7 + B – 10 = A

∴ B – A = 3 … (3)

For ten’s place,

B + A + 1 = 8

∴ B + A =7 …(4)

Solving 3 and 4 simultaneously,

2B = 10

∴ B = 5 and A = 2