My number is a 2-digit multiple of 9. the ratio of its units digit to its tens digit is 1: 2. what is my number?

The answer is:  63  .

Explanation:

First, let's list all the 2-digit multiples of "9":

18, 27, 36, 45, 54, 63, 72, 81, 90, 99.

From this list, the only answer that has a ratio in which its "units digits to its tens digits" is "1:2"  is:  "63" .   "3:6"  = "1:2" .

So the answer is:  63 .