The table shown summarizes the number of employees at each of the 17 restaurants in a town.
| Number of employees | Number of restaurants |
|---|---|
| 2 to 7 | 2 |
| 8 to 13 | 4 |
| 14 to 19 | 2 |
| 20 to 25 | 7 |
| 26 to 31 | 2 |
Which of the following could be the median number of employees for the restaurants in this town?
2
9
15
21
