Sarah notices the number of ounces of water drunk varies directly with how many glasses she drinks. on thursday she drank 6 glasses of water, which resulted in 66 ounces of water. her goal tomorrow is 132 ounces, or _ glasses of water.

Her goal is to drink 12 glasses of water, because the question tells us that every glass of water has the same amount of ounces. If she drank 6 glasses and there's 66 ounces in total, all we have to do to get the amount of ounces per glass is divide 66 by 6 to get 11. Therefore, we know that the total amount of ounces divided by the amount of ounces per glass is the amount of glasses, and 132 divided by 11 is 12.