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:
| Team | Tries for | Tries against | Try diff | Points for | Points against | Points diff |
| --- | --- | --- | --- | --- | --- | --- |
| Castres Olympique | 29 | 6 | +23 | 207 | 71 | +136 |
| Narbonne | 21 | 6 | +15 | 161 | 90 | +71 |
| Dinamo-Bucureşti | 12 | 32 | −20 | 109 | 213 | −104 |
| Bridgend | 10 | 14 | −4 | 94 | 120 | −26 |
| Bristol Shoguns | 11 | 12 | −1 | 128 | 99 | +29 |
| Treorchy | 10 | 23 | −13 | 72 | 178 | −106 |
| Source : www.ercrugby.com | Source : www.ercrugby.com | Source : www.ercrugby.com | Source : www.ercrugby.com | Source : www.ercrugby.com | Source : www.ercrugby.com | Source : www.ercrugby.com |
Question:
What is Tries Against, when Tries For is 21?
Answer:
6.0