Police recorded the average speed of cars driving on a busy street by a school For a sample of 36 speeds it was determined that the average amount over the speed limit for the 36 speeds w 12 6 mph with a standard deviation of 9 mph The 95 confidence interval estimate for this sample is 9 55 mph to 15 65 mph a What is the margin of error for this problem b What size sample is needed to reduce the margin of error to no more than 2