Hi!
For starters, there are 128 ounces in a gallon. Knowing there are 3 gallons we want to multiply this by 3. 128 x 3 = 384 ounces.
Now, each cup can hold 12 ounces. Therefore we want to divide 384 by 12. 384/12 = 32. Therefore Mr. Cruz can completely fill 32 cups with water from the cooler.
Hope this helps! :D
Let me know if you need help with anything else :0)