Answer:
If it's hours total, then 20 hours total to fill.
Step-by-step explanation:
If it was filled 5 gallons an hour for 10 hours, 5 times 10=50
So there's 50 gallons out of the 100 gallons filled before the animals drank
If the animals drank 2 gal/h with it still being filled at 5 gal/h FOR 5 HOURS, you subtract the 25 (5 gal/h times 5 hours) by 10 (2 gal/h times 5 hours) to get how much gallons were filled in that time span, which is 15
Since he added a hose that filled at 4 gal/h, you can infer that, in total, it is now 9 gal/h because you add 5+4.
The animals are still going to drink at 2 gal/h, so you subtract 9 from 2 and get 7 gallons filling up the pool per hour.
Since you have 35 gallons left (you already filled 65 gallons), you can divide the 35 by 7 to get 5 hours.