So basically it says every 1/4 cup of water, you need 3/4 cups of orange juice. Now, 1 cup of water is the same thing as 4/4 cups of water. To get to 4/4 from 1/4, you need to multiply 1/4 by 4. Because of that, you need to multiply 3/4 by 4 as well. 3/4 * 4 is 3, and that's how you get your answer.
