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:
|  |  | 2018 | 2017 | 2016 |
| --- | --- | --- | --- | --- |
| Compensation cost: | RSUs | $98 | $63 | $58 |
| Compensation cost: | Restricted stock | 2 | 8 | 11 |
| Compensation cost: | Stock options | 1 | 2 | 1 |
| Compensation cost: | Total | $101 | $73 | $70 |
Question:
What was the cost of restricted stock units awarded by United Airlines in 2017?
Answer:
$63