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:
| Driver | Constructor | Laps | Time/retired | Grid |
| --- | --- | --- | --- | --- |
| Alberto Ascari | Ferrari | 20.0 | 3:23:03.3 | 1.0 |
| Juan Manuel Fangio | Alfa Romeo | 20.0 | +30.5 | 3.0 |
| José Froilán González | Ferrari | 20.0 | +4:39.0 | 2.0 |
| Luigi Villoresi | Ferrari | 20.0 | +5:50.2 | 5.0 |
| Piero Taruffi | Ferrari | 20.0 | +7:49.1 | 6.0 |
| Rudi Fischer | Ferrari | 19.0 | +1 lap | 8.0 |
| Robert Manzon | Simca-Gordini | 19.0 | +1 lap | 9.0 |
| Louis Rosier | Talbot-Lago - Talbot | 19.0 | +1 lap | 15.0 |
| Pierre Levegh | Talbot-Lago - Talbot | 18.0 | +2 laps | 19.0 |
| Jacques Swaters | Talbot-Lago - Talbot | 18.0 | +2 laps | 22.0 |
| Johnny Claes | Talbot-Lago - Talbot | 17.0 | +3 laps | 18.0 |
| Yves Giraud Cabantous | Talbot-Lago - Talbot | 17.0 | Accident | 11.0 |
| Maurice Trintignant | Simca-Gordini | 13.0 | Engine | 14.0 |
| Felice Bonetto | Alfa Romeo | 12.0 | Magneto | 10.0 |
| Duncan Hamilton | Talbot-Lago - Talbot | 12.0 | Oil pressure | 20.0 |
| Paul Pietsch | Alfa Romeo | 11.0 | Accident | 7.0 |
| André Simon | Simca-Gordini | 11.0 | Engine | 12.0 |
| Nino Farina | Alfa Romeo | 8.0 | Overheating | 4.0 |
| Philippe Étancelin | Talbot-Lago - Talbot | 4.0 | Gearbox | 21.0 |
| Louis Chiron | Talbot-Lago - Talbot | 3.0 | Ignition | 13.0 |
| Toni Branca | Maserati | 3.0 | Engine | 17.0 |
| Toulo de Graffenried | Maserati | 2.0 | Engine | 16.0 |
Question:
what is the time/retired when the grid is less than 13, the constructor is alfa romeo and the laps is more than 12?
Answer:
30.5