Well, isn't that just a happy little question! When we add 12 and 9 together, we get 21. Just imagine those numbers coming together like old friends, creating a beautiful sum that brings a smile to your face.
The sum of 12 and 9 is 21. In mathematics, the sum is the result of adding two or more numbers together. In this case, when you add 12 and 9, you get a total of 21.