Answer: He should use 14 fluid ounces of soap.
Step-by-step explanation:
1. You need to make the conversion from cups to ounces.
You know that:
[tex]1\ cup = 8\ fluid\ ounce[/tex]
Then:
[tex](3\ cups)(\frac{8\ fluid\ ounce}{1\ cup})=24\ fluid\ ounce[/tex]
2. According to the information given in the exercise, Kevin must use 4 fluid ounces of concentrated soap for every 3 cups of water or 24 fluid ounces of water.
Then, knowing that he uses 84 fluid ounces of water to make an all-purpose cleaner, you can set up the following proportion:
[tex]\frac{4}{24}=\frac{x}{84}[/tex]
Where "x" is the total fluid ounces of soap that Kevin should use.
3. Solving for "x", you get this result:
[tex](84)(\frac{4}{24})=x\\\\x=14[/tex]