Answer: 6 hours
Step-By-Step Explanation: The difference in the rate of Pool A and Pool B is 3 gallons per hour. That means that every hour, Pool A gains 3 gallons on Pool B which means by 5 hours, the 15-gallon difference will be equal. Since the question is asking for more than not equal, it's required for 1 more hour for Pool A to be greater than pool B