Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Volume | Discs | Episodes | Region 1 release | Region 2 release | Region 4 release |
| --- | --- | --- | --- | --- | --- |
| 1 | 1.0 | 5.0 | January 23, 2007 | Not released | June 4, 2009 |
| 2 | 1.0 | 5.0 | April 10, 2007 | Not released | August 6, 2009 |
| 3 | 1.0 | 5.0 | May 22, 2007 | Not released | October 29, 2009 |
| 4 | 1.0 | 5.0 | August 14, 2007 | Not released | March 31, 2010 |
| Box set | 4.0 | 20.0 | September 11, 2007 | July 20, 2009 | September 9, 2010 |
Question:
What is the average episode that has September 11, 2007 as a region 1?
Answer:
20.0