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 |
| --- | --- | --- | --- | --- |
| Juan Manuel Fangio | Maserati | 77.0 | 3:07:46.4 | 1.0 |
| Luigi Musso | Ferrari | 77.0 | +50.8 secs | 3.0 |
| Peter Collins | Ferrari | 77.0 | +2:06.0 | 5.0 |
| Mike Hawthorn | Ferrari | 76.0 | +1 Lap | 7.0 |
| Harry Schell | Maserati | 70.0 | +7 Laps | 4.0 |
| Jean Behra | Maserati | 69.0 | +8 Laps | 2.0 |
| Mike MacDowel Jack Brabham | Cooper - Climax | 68.0 | +9 Laps | 15.0 |
| Carlos Menditeguy | Maserati | 30.0 | Engine | 9.0 |
| Stuart Lewis-Evans | Vanwall | 30.0 | Steering | 10.0 |
| Roy Salvadori | Vanwall | 25.0 | Engine | 6.0 |
| Herbert MacKay-Fraser | BRM | 24.0 | Transmission | 12.0 |
| Maurice Trintignant | Ferrari | 23.0 | Electrical | 8.0 |
| Jack Brabham | Cooper - Climax | 4.0 | Accident | 13.0 |
| Horace Gould | Maserati | 4.0 | Halfshaft | 14.0 |
| Ron Flockhart | BRM | 2.0 | Accident | 11.0 |
Question:
What is the lap total for the grid under 15 that retired due to transmission?
Answer:
24.0