The sum of the digits of a two-digit number is 9 if the digits are reversed the new number is 9 more than the original number?

Possibility of two digit no whose sum is 9

18,27,36,45,54,63,72,81

Now add 9 to each no mentioned above

27,36,45,54,63,72,81,90

See after 3rd comma 45 and 54. reverse of 45 is 54. 54 is 9 more than 45. So 45 is the original