A car driving at 20 m/s is approaching a stoplight. As the stoplight turns red, the driver decides that the car is going too fast to stop at the white line and hits the brakes hard. The tires screech as the car decelerates at a constant rate. When the car reaches 3/6 of the distance to the white line, the driver is confident that the speed of the car is under control and eases off the brake pedal. The car decelerates at 1/5 the rate for the remaining 3/6 of the distance and stops on the white line.
How fast was the car going when the driver changed the rate of deceleration?