A vehicle's stopping distance is equal to:

The stopping distance of a vehicle is defined as the total distance it takes for a vehicle to come to a complete stop from the time a driver recognizes a need to stop until the vehicle is fully stopped. This distance is critically important for safe driving and varies depending on several factors, including speed, road conditions, and the driver's response time.

The correct option states that stopping distance is the sum of the braking distance and the reaction distance. The reaction distance is the distance traveled while the driver is reacting to a stimulus (like seeing a stop sign or a pedestrian). This includes the time it takes a driver to move their foot from the accelerator to the brake pedal and the time taken to actually apply the brakes. Once the brakes are applied, the braking distance is the distance the vehicle travels while coming to a stop from the moment the brakes are engaged.

The combination of both of these distances—reaction distance before the brakes are applied and braking distance after—provides a comprehensive measure of how far the vehicle travels before it stops completely, making this understanding vital for safe driving practices.