[tex] \frac{42}{1} * \frac{1}{7} to get the amount of gallons per week to gallons per day. The \frac{42}{1} is 42 gallons per week, and \frac{1}{7} is taking that 42 gallons per week and making it x gallons per day by dividing the 42 per week by 7 since there are 7 days in a week.
Multiply the gallons per day (6) by 3 for the amount of days you are trying to figure out to get:
A final answer of 18 gallons per day.