Why pick 13? Because the total must come to 39. You will make a mistake if you use 11 rather than 13. You must include the cleaner in the denominator. Very tricky question.
So the final answer is
Cleaner: 6
Water: 39 - 6 = 33 pints of water.
Very few of your classmates will get this if they are not in chemistry. You might even be told your answer is incorrect. It isn't.