You could do this the simple way which is to first grab two numbers in any order and add them together, and after you do that you can add the result to the remaining number or numbers that remain. 9.94 plus 1 is 10.94, and 10.94 plus 19 is 29.94, lastly the .1 from the 19 which finally leads us to the answer of 30.04 gallons that Boris bought last week
