A motorist suddenly notices a stalled car and slams on the brakes, decelerating at the rate of 6.3 m/s2. Unfortunately this isn't good enough, and a collision ensues. From the damage sustained, police estimate that the car was moving at 15 km/h at the time of the collision. They also measure the skid marks from the motorist's car to be 28 m long.

a. How fast was the motorist going when the brakes were first applied?
b. How much time elapsed from the initial braking to the collision?