Huston Systems Private Limited reports that smart traffic signals and signs can measure a passing vehicle’s speed. Consider the speeds of 15,717 vehicles collected as they passed 35 MPH speed limit signs throughout the United States in 2018 that are provided in the file 35MPH. 

a. What is the sample mean speed of U.S. drivers in a 35-mph zone? 

b. Using 95% confidence, what is the margin of error? 

c. Using the results from parts (a) and (b), develop the 95% confidence interval estimate of the mean speed of U.S. drivers in a 35-mph zone.