Anna used 900 gallons of gasoline last year driving to and from work. this year, she changed jobs. she now uses only 600 gallons of gas annually.
if each gallon of gas releases 20 pounds of co2 when burned, anna reduced her co2 emissions by

The answer is 3.33%. Anna reduced her CO2 emissions by 3.33% from using 600 gallons of gas annually than from using 900 gallons of gasoline annually. I arrived to this answer through multiplying gallons by 20 pounds of C02 (600*20) = 12000; (900*20) = 18000. Then I proceeded to subtract 12000 from 18000 which yielded me 600 (18000-12000 = 600). Lastly, I divided 600 by 18000 and it gave an answer of .0333. Then, I converted it to percent, thus, yielding me the answer of 3.33%.

Where is the qeustion

No solution : there is no number of boxes that she bought