22.5 cups of water
First off, since we know that 9 cups of water is used for every 2 cups of rice. We can just double 9 to make 18, which would now count as 4 cups of rice.
Then you would half the 9 cups of water to find out how many cups of water is used for 1 cup of rice, which is 4.5.
Add them up you get 22.5
