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:
| Type | Seats | Average Age (Yrs) | Number of Aircraft | Number Owned (a) | Number Leased |
| --- | --- | --- | --- | --- | --- |
| 737-700 | 143 | 14 | 512 | 397 | 115 |
| 737-800 | 175 | 3 | 181 | 174 | 7 |
| 737 MAX 8 | 175 | — | 13 | 13 | — |
| Totals |  | 11 | 706 | 584 | 122 |
Question:
What is the average age of planes used by Southwest in 2017?
Answer:
11