1. Referring to sheet 'Topic 1Interval Estimates' in the data file answer the following questions. A. Based on the sample of 50 students, calculate the point estimate for the average $ that students spend on their cell phones and the standard deviation of that average. Make sure you're using the right variable for this problem. There are two variables in the sheet, but only one makes sense to use. B. Construct a 90% confidence interval around this point estimate. (Assume you don't have a good estimate for the population standard deviation, so you have to estimate it using the sample standard deviation. Accordingly, make sure you use the t distribution when calculating the confidence interval.) C. Interpret the results of part b). What does your interval estimate tell you? D. Now assume your clients want a smaller confidence interval, with a margin of error that's no bigger than 296. How big would your new sample have to be? (Use the standard deviation you calculated in part A, as a planning value for the population standard deviation.)