Taxable synthetic natural gas

"Taxable synthetic natural gas" does not include synthetic natural gas used within the plant and does not include any amount of synthetic natural gas in excess of one hundred ten million cubic feet per day, over and above that used within the plant. Calculation of any amount of synthetic natural gas in excess of one hundred ten million cubic feet per day must be accomplished by multiplying one hundred ten million cubic feet by the number of days in the month for which the report is filed, and subtracting the result from the total number of cubic feet of synthetic natural gas produced, less that used within the plant, during the month for which the report is made.