Does it matter if any one tank is empty in 4 hours?
Are you trying to determine if you are using to much of what is in the tank over 3 hours?
Does it matter if any one tank is empty during the 3 hours?
As the question was asked you cannot go less than 24.3% of 2000 combined. 2 tanks can be empty and the other tank have 1458.01lbs in it with no fault...
Unusual to have 2 tanks empty and another more than half full and be ok.