When a driver brings a car to a stop by braking as hard as possible, the stopping distance can be regarded as the sum of two distances:
"reaction distance", which is initial speed times reaction time, and "braking distance," which is the distance covered during braking.
The following table gives typical values of these:

Initial speed (m/s) Reaction distance (m) Braking distance (m) Stopping distance (m)
10 7.5 5.0 12.5
20 15 20 35
30 22.5 45 67.5

(a) What reaction time is the driver assumed to have?
(b) What is the car's stopping distance if the initial speed is 251 m/s?