112. In a recent sample of 84 used car sales costs, the sample mean was $6,425, with a standard deviation of $3,156. Assume the underlying distribution is approximately normal. a. Which distribution should you use for this problem? Explain your choice. b. Define the random variable X in words. c. Construct a 95 percent confidence interval for the population mean cost of a used car. i. State the confidence interval. ii. Sketch the graph. iii. Calculate the error bound. W means for this study.