This can be calculated easily.
As any two digit number can be written in the following form:
N= 10x +y
If we reverse the number now, it would become:
N' = 10y + x
So if we subtract one from the other, we should obtain 18 ( as mentioned in the question ).
N-N'= 18
=> x-y = 2
Thus, any number whose digits differ by two would be an aswer to the question.
The only numbers which satisfy this are : 13,24,35,46,57,68,79
But this would not be true for any 3 or more digit number.
