you can either solve going from cups to gallons first or days to week. if you do days first there are 7 days in a week. so by multiplying 1.5 cups by 7 days in a week you get how many cups per week. then convert that number of cups to gallons. there are 16 cups in 1 gallon so divid the number of cups per week by 16 and you will get gallons per week