Question

HELP ! check out attachment in comment box
is it A. ?

Answer 1

Remember you can write a two digit number 45 = 4*10 + 5
Let a > b
You can write ab = a*10 + b.
So the question asks ab-ba
ab-ba = a*10 + b - b*10 - a = 9a-9b = 9(a-b) which is divisible by 9.