First you can see that at 30% we have 651 gallons so you want to multiply it by three because we are trying to get to 100% after you multiply it by three we have found out how much it is filled at 90% which is 1953 so then you want to divide 651 by 3 because all we need is 10 more percent to make it to 100% and 1/3 of 30% is 10% and 10% of 651 is 217. Finally all you have to do is add 217 and 1953 and you get 2,170 gallons.
