Here, in tens place,

6 – 3 = 3

Which implies that maximum value of A is 3

Ie. A ≤ 3

Now in units place,

A - B = 7

This states that borrowing is involved.

∴ in tens place,

6 – A – 1 = 3

∴ A = 2

Now in units place,

A + 10 – B = 7 …as borrowing is involved

∴ 12 – B = 7

∴ B = 5