He sum of the digits of a certain two digit number is 9 when you reverse its digits you decrease the number by 45 find the number

7 + 2 = 9

72 - 45 = 27

Therefor the number is 72

I just solved this by trial and error but there are some obvious values that won't work like 81 and 90 are too big whilst 63 and 54 are too small so 72 is left

27 and 72.

You can get this mostly just by trying the different 2 digit numbers that combine to 9.