The speed of cars on a certain motorway has a normal distribution with mean 90 km/hr and a standard deviation of 12 km/hr. A radar unit is used to measure speeds of cars on this motorway. On a particular day, 9 cars are picked up at random on this motorway and their speeds are measured. a. What is the distribution of the mean speed of the cars in this sample? b. What is the probability that the sample mean will be greater than 96 km/hr? c. What is the probability that the sample mean will be less than 88 km/hr?