Answer:
IF each hour is 6,000 gallons drained then two hours would be 12,000 because 6 + 6=12 so 6,000+6,000=12,000 so for it to be at 18,000 then you have to add 6 more or 6,000 more so 6,000+6,000+6,000 =18,000 so the awnser would be 3 hours.
Step-by-step explanation: