So as you know, one gallon has 16 cups, and there's 7 days in a week. So, if you multiple 1.5 by 7 you would get 10.5 cups per week, then divide that by 16 and get .65625 gallons per week.
here is the answer I just took a picture because I already answered this for someone eles
1 gallon = 16 cups
1 hour = 60 min
16 cups = 60 min
5 gallons =180 min/ 3 hrs
1 cup = 3.75 minutes