The question is 1/3 ( x + 9 ) = 12. You want to find out the value of x.
The way I sometimes teach the idea behind solving an equation is to first walk through it step-by-step in words:
1. This statement is telling you that one-third of the value of x + 9 is equal to 12. Let's call x + 9 an expression.
2. If one third of any expression is equal to 12, then the entire expression must be equal to 36 (because you need three thirds to get to a whole, and 3 times 12 will get you to 36, won't it?) So now we've gotten rid of the 1/3 part and can just say x + 9 is equal to 36.
3. If 9 and something is equal to 36, we can take 9 away from 36 to find out what that is (real quick, take ten away from 36 and then add one back).
4. The answer is 27. x = 27.