18 The diagram is the speed-time graph for 25 seconds of a car’s journey. The car slows down uniformly from a speed of v m/s to a speed of 12 m/s in 15 seconds. It then travels at constant speed for a further 10 seconds. (a) The retardation of the car is 0.4 m/s2. Calculate the value of v. (b) Calculate the distance travelled by the car from t = 0 to t = 25.