Answer:
Step-by-step explanation:
Alright, lets get started.
At 9:30 AM , he started filling the pond and at 12:30 PM means, after 3 hrs, he had filled 2100 gallons.
Means,
2100 gallons can be filled in time = 
So, 1 gallon can be filled in time = 
Hence, 3500 gallons can be filled in time = 
Hence, 3500 gallons can be filled in time = 
Means it will take 5 hrs to fill the pond.
So after 5 hrs, time will be : 
The time will be :
: Answer
Hope it will help :)