title: 2015 6 Hours of Silverstone
context: Twenty-nine cars were officially entered for the 6 Hours of Silverstone with most of the entries in the Le Mans Prototype 1 (LMP1) and Le Mans Prototype 2 (LMP2) classes.[1][2] The 2014 race winners, Toyota, returned to defend their title. Three manufacturers, Porsche, Toyota and Audi Sport Team Joest, were represented in LMP1 by two cars each. Team ByKolles were the sole LMP1 privateer team partaking in the race.[2] Nissan were scheduled to debut two GT-R LM Nismos at the circuit but decided to forego the season's opening two rounds after issues with the vehicle during testing. The team decided to focus on making its debut at the 24 Hours of Le Mans.[3] Similarly, Rebellion Racing signed a contract to run Advanced Engine Research V6 twin-turbocharged engines instead of Toyota V8s they had used since 2012. This prompted the outfit to withdraw from the season's first two races so they and chassis developer Oreca could adapt the R-Ones for the new engine.[4] After the retirement of nine-time 24 Hours of Le Mans winner Tom Kristensen, Audi internally promoted Oliver Jarvis to the squad.[5] ByKolles's Simon Trummer was stranded in Switzerland due to a French air traffic control strike, and Christian Klien was contacted on the day of the first practice session to take his place.[6]
question: How many cars participated in the 2015 6 Hours of Silverstone race?
answers: Twenty-nine