what is the average discounted cash flow balance for the three year period , in millions?
Important information:
text_0: 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 ) .
table_12: ( in millions ) the beginning of the year of 2008 is 13495 ; the beginning of the year of 2007 is 8518 ; the beginning of the year of 2006 is 10601 ;
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 ;
Reasoning Steps:
Step: average1-1(end of year, none) = 8872
Program:
table_average(end of year, none)
Program (Nested):
table_average(end of year, none)

Please answer the following financial question based on the context provided. Make sure to give the answer in raw number, not in percentage and without any units. If the question asks for percentage the value should be less than 1
Context:
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 ) .
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 )  
.
Question: 
what is the average discounted cash flow balance for the three year period , in millions?
Important information:
text_0: 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 ) .
table_12: ( in millions ) the beginning of the year of 2008 is 13495 ; the beginning of the year of 2007 is 8518 ; the beginning of the year of 2006 is 10601 ;
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 ;
Reasoning Steps:
Step: average1-1(end of year, none) = 8872
Program:
table_average(end of year, none)
Program (Nested):
table_average(end of year, none)
