To get the previous population you would have to multiply 9,300 by 38% (.38) and then add it to 9,300, or you can also multiply it by 138% (1.38) and still get the same answer but this step is only a one step the first is a two step process
First you need to know how many pounds of carbon dioxide you get when burning 1 gallon of gasoline. That number is 19.64 pounds
To get the number of pounds released when entire tank is burned you need to multiply gas tank volume and number of pounds you get when 1 gallon is burned.