Table:
|  | Number of Shares | Weighted-Average Exercise Price Per Share | Weighted-Average Remaining Contractual Life (In Years) | Aggregate Intrinsic Value |
| --- | --- | --- | --- | --- |
| Outstanding as of August 30, 2018 | 18 | $23.38 |  |  |
| Granted | — | 44.30 |  |  |
| Exercised | (5) | 17.50 |  |  |
| Canceled or expired | (1) | 22.60 |  |  |
| Outstanding as of August 29, 2019 | 12 | 25.94 | 4.3 | $220 |
| Exercisable as of August 29, 2019 | 7 | $25.37 | 3.7 | $143 |
| Unvested as of August 29, 2019 | 5 | 26.94 | 5.5 | 77 |
Paragraphs:
Stock Options
Our stock options are generally exercisable in increments of either one-fourth or one-third per year beginning one year from the date of grant. Stock options issued after February 2014 expire eight years from the date of grant. Options issued prior to February 2014 expire six years from the date of grant. Option activity for 2019 is summarized as follows:
The total intrinsic value was $108 million, $446 million, and $198 million for options exercised in 2019, 2018, and 2017, respectively.
Question:
How are the stock options generally exercised?
Answer: in increments of either one-fourth or one-third per year beginning one year from the date of grant