Multiply 1.5 times 7. That comes to 10.5 cups per week. Now convert it to quarts. There are 4 cups in one quart, so divide 10.5 by 4. That comes to 2.625 quarts per week. Now convert it to gallons. There are 4 quarts in a gallon, so divide 2.625 by 4. That comes to about 0.7 gallons a week, or 7/10.
