The proper way to do this is to set up an equation for the number you're trying to find. Any thoughts on what that equation might be?
Yes, that's right- though this is a strange way of putting it! It took me a moment to realize that you were using "/" as a 'separator', not meaning division. You are saying, "The answer is 162. 36 divided by 2 = 18." (not "81"- that was a typo). But now I am confused. You say "18 divided by 9 is 2." And therefore ???? Where did "162" come from.
In fact, the problem is "2/ 9 of a number is 36". That is, if you multiply a number by 2 and then divide by 9, you get 36. Okay, to go back to the number work backwards! Instead of multiplying by 2, divide by 2: 36 divided by 2 is 18, just as you say. Instead of dividing by 9, multiply by 9: 18 times 9 is 162.