Answer:
3/5 cup
Explanation:
I start by changing the initial fraction of 3/4 into its decimal form of .75 so that it's easier to divide. I then divide it by 5 to find how much carbonated water you should use for a single cup of juice, which is .15 cups. Then, I multiply .15 times 4, which comes out to be .6, or 3/5.