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:
|  |  | Twelve Months Ended December 31, | Twelve Months Ended December 31, | Twelve Months Ended December 31, |
| --- | --- | --- | --- | --- |
|  |  | 2016 | 2015 | % Change |
| Passenger | Mainline | $4,098 | $3,939 | 4.0% |
| Passenger | Regional | 908 | 854 | 6.3% |
| Passenger | Total passenger revenue | $5,006 | $4,793 | 4.4% |
| Passenger | Freight and mail | 108 | 108 | —% |
| Passenger | Other—net | 817 | 697 | 17.2% |
| Passenger | Total operating revenues | $5,931 | $5,598 | 5.9% |
Question:
By how much did Alaska's mainline passenger revenue increase from 2015 to 2016?
Answer:
4.0%