{"pre_text": ["supplementary information on oil and gas producing activities ( unaudited ) c o n t i n u e d summary of changes in standardized measure of discounted future net cash flows relating to proved oil and gas reserves ( in millions ) 2008 2007 2006 sales and transfers of oil and gas produced , net of production , transportation and administrative costs $ ( 7141 ) $ ( 4887 ) $ ( 5312 ) net changes in prices and production , transportation and administrative costs related to future production ( 18290 ) 12845 ( 1342 ) ."], "post_text": ["."], "table": [["( in millions )", "2008", "2007", "2006"], ["sales and transfers of oil and gas produced net of production transportation and administrative costs", "$ -7141 ( 7141 )", "$ -4887 ( 4887 )", "$ -5312 ( 5312 )"], ["net changes in prices and production transportation and administrative costs related to future production", "-18290 ( 18290 )", "12845", "-1342 ( 1342 )"], ["extensions discoveries and improved recovery less related costs", "663", "1816", "1290"], ["development costs incurred during the period", "1916", "1654", "1251"], ["changes in estimated future development costs", "-1584 ( 1584 )", "-1727 ( 1727 )", "-527 ( 527 )"], ["revisions of previous quantity estimates", "53", "290", "1319"], ["net changes in purchases and sales of minerals in place", "-13 ( 13 )", "23", "30"], ["accretion of discount", "2796", "1726", "1882"], ["net change in income taxes", "12805", "-6751 ( 6751 )", "-660 ( 660 )"], ["timing and other", "-96 ( 96 )", "-12 ( 12 )", "-14 ( 14 )"], ["net change for the year", "-8891 ( 8891 )", "4977", "-2083 ( 2083 )"], ["beginning of the year", "13495", "8518", "10601"], ["end of year", "$ 4604", "$ 13495", "$ 8518"], ["net change for the year from discontinued operations", "$ 2013", "$ 2013", "$ -216 ( 216 )"]], "table_ori": [["<i>(In millions)</i>", "2008", "2007", "2006"], ["Sales and transfers of oil and gas produced, net of production, transportation and administrative costs", "$(7,141)", "$(4,887)", "$(5,312)"], ["Net changes in prices and production, transportation and administrative costs related to future production", "(18,290)", "12,845", "(1,342)"], ["Extensions, discoveries and improved recovery, less related costs", "663", "1,816", "1,290"], ["Development costs incurred during the period", "1,916", "1,654", "1,251"], ["Changes in estimated future development costs", "(1,584)", "(1,727)", "(527)"], ["Revisions of previous quantity estimates", "53", "290", "1,319"], ["Net changes in purchases and sales of minerals in place", "(13)", "23", "30"], ["Accretion of discount", "2,796", "1,726", "1,882"], ["Net change in income taxes", "12,805", "(6,751)", "(660)"], ["Timing and other", "(96)", "(12)", "(14)"], ["Net change for the year", "(8,891)", "4,977", "(2,083)"], ["Beginning of the year", "13,495", "8,518", "10,601"], ["End of year", "$4,604", "$13,495", "$8,518"], ["Net change for the year from discontinued operations", "$–", "$–", "$(216)"]]}

Question: what is the average discounted cash flow balance for the three year period , in millions?
Evidence:
table_13: ( in millions ) the end of year of 2008 is $ 4604 ; the end of year of 2007 is $ 13495 ; the end of year of 2006 is $ 8518 ;
Program: table_average(end of year, none)
Answer:
str_answer: 8872
exe_answer: 8872.33333