How many hours will it take to drain the basement? the top question

So hmm notice the picture below

bear in mind that width is 28' 6", now, 6 inches is just half a foot, so is just 28.5' or 28.5 feet

anyhow... now we know how many ft³
however, the pumps are pumping out at gallons per minute

well, how many gallons are in the basement then? that is
what is 20520 ft³ in gallons?

well, 1ft³ is 7.48US gallons
so 20520 ft³ si 20520 * 7.48 gallons, or 153489.6 gallons

now, you have two pumps, each doing 12 gallons per minute
so, every minute is 24 gallons being pumped out of the basement then

if 24 gallons are done in 1minute, how long for 153489.6 gallons?



now, to convert that to hours, simply divide it by 60
recall, there are 60minutes in 1hr