Two fair 6-sided dice are rolled. what is the probability the sum rolled is 9?

The probability is

        (number of ways to roll a 9) / (total possible different rolls) .

Each cube can land in 6 different ways, so the total possible rolls = 36 .

How many different rolls can be a sum of 9 ?
I don't know.  Let's countum:

Cube-A  Cube-B
     3            6
     4            5
     5            4
     6            3

Did I miss any ?  I don't think so.  There are four (4) ways to roll a 9.

So the probability is      4 / 36  =  1/9  =  11.1%