Since there is 16 cups in a US gallon, and there is 7 days in a week. First, you would multiply 1.5 times 7 getting 10.5 cups. But since that is not enough cups to be a gallon the division equation would look like this, 10.5/16 = ?. You can simplify it down to 5.25/8. Then, you get your answer of 0.65625 gallons.
