Final answer:
Hill start assist in cars holds the brakes for around 2 to 3 seconds to prevent the car from rolling backwards when starting on an incline.
Step-by-step explanation:
Hill start assist is a feature in cars that helps prevent them from rolling backwards when starting on an incline. This feature holds the brakes for a certain amount of time to allow the driver to switch from the brake pedal to the accelerator pedal without the car rolling backwards. The time that hill start assist holds the brakes can vary depending on the specific car model, but it is typically around 2 to 3 seconds.