How do you solve this confusing Ratio and Proportions question?

Question

Water needs to be removed from an underground chamber before work can commence. When the water was at a depth of 3m, five suction pipes were used and emptied the chamber in 4 hours. If the water is now at a depth of 5m (same cross- section), and you want to empty the chamber in 10 hours time, how many pipes need to be used?

Please explain this to me like I've never done a ratio problem before, this question is very confusing to me.

Answer 1

Let's assume that each meter depth holds 1000 gallons of water (this is arbitrary, any positive number works!)

So, initially with 3 meters, there is 3000 gallons to be pumped in 4 hours. So 3000/4 = 750 gallons/hour but if 5 pipes are used, then each pipe pumps 750/5 = 150 gallons/hour

Next, 5 meters implies that there is 5000 gallons to be pumped. Over 10 hours, this equates to

5000/10 = 500 gallons per hour. But we know that each pipe pumps 150 gallons/hour

So, 500/150 = 3.33 pipes needed or 4 pipes if it needs to be 10 hours or less.