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:
|  | Increase (decrease) from 2017 (a): | Increase (decrease) from 2017 (a): | Increase (decrease) from 2017 (a): | Increase (decrease) from 2017 (a): | Increase (decrease) from 2017 (a): |  |
| --- | --- | --- | --- | --- | --- | --- |
|  | Domestic | Atlantic | Pacific | Latin | Total | Increase (decrease) from 2017 (a): |
|  |  |  |  |  |  |  |
|  |  |  |  |  |  | Domestic |
|  |  |  |  |  |  | Atlantic |
| Passenger revenue (in millions) | $2,340 | $688 | $185 | $33 | $3,246 |  |
| Passenger revenue | 11.1% | 11.7 % | 4.3 % | 1.0 % | 9.4% |  |
| Average fare per passenger | 2.8% | 0.2 % | 8.5 % | 2.5 % | 2.3% |  |
| Yield | 3.8% | (0.4)% | 2.7 % | (0.3)% | 2.8% |  |
| PRASM | 4.1% | 6.3 % | 3.0 % | 0.8 % | 4.3% |  |
| Passengers | 8.1% | 11.5 % | (3.9)% | (1.4)% | 6.9% |  |
| RPMs (traffic) | 7.0% | 12.1 % | 1.5 % | 1.3 % | 6.4% |  |
| ASMs (capacity) | 6.7% | 5.1 % | 1.3 % | 0.3 % | 4.9% |  |
| Passenger load factor (points) | 0.2 | 5.1 | 0.2 | 0.8 | 1.2 |  |
| 11 |  |  |  |  |  | (a) See Part II, Item 6, Selected Financial Data, of this report for the definition of these statistics. |
Question:
How much did United Airlines' revenue passenger miles change between 2017 and 2018?
Answer:
6.4%