An 800 gallon swimming pool is being drained. After five hours, 500 gallons have been drained. If the rate of drainage continues, how long will it take to drain the pool?

A) 0.125 hours

B) 5 hours

C) 8 hours

D) 9 hours

I think it's 8 hours. If it takes 5 hours to drain 500 gallons, then the rate is 100 gallons drained per hour. So if it continues at this rate, the remaining 300 gallons would be drained in three hours, plus the five spent on the other 500 gallons, so it would be 8 hours for all 80p gallons to empty the swimming pool.