Carrie started with 12 ounces of water when she began her walk. When she was finished walking she had 2 1/4 ounces of water left. How much did she drink?

We are given with an initial value of water equal to 12 ounces of water and the final value of water is 2 1/4 or 2.25 ounces. Since the two substances are the same, we can use direct subtraction to determine what was consumed after walking. The answer is 12-2.25 equal to 9.75 ounces