AFCAT I 2017 Solved Paper

A number is divisible by 9 when the sum of its digit isdivisible by 9.
So, (3 + 8 + 1 + A) = must be divisible by 9.
Thus smallest natural number be 6.
or, (3 + 8 + 1 + 6) = 18, this is divisible by 9.