In the first 4 hours, the milk tanker got 4 hours * 2880 gallons/hour = <<4*2880=11520>>11,520 gallons
Thus, the storage tank was left with 30,000 gallons - 11,520 gallons = <<30000-11520=18480>>18,480 gallons.
For the next 7 hrs, the workers added 1,500 gallons/hour * 7 hours = <<1500*7=10500>>10,500 gallons
The total therefore is 18,480 gallons + 10,500 gallons = <<18480+10500=28980>>28,980 gallons
#### 28,980