What is a 95-percent confidence interval for the mean one year extended warranty expenditure per automobile?

Five years ago, an automobile manufacturer started offering an extended warranty to buyers of its sport utility vehicle. The extended warranty covered defects occurring after the initial three year warranty expired. Of the 10,000 people who bought the sport utility vehicle in the first year of the program, 15 percent purchased the extended warranty.
In the warranty department, you have recently received data on a random sample of 200 of the cars sold in the first year that the extended warranty was available. For this sample, the average extended-warranty expenditure per car for the one year period after the initial warranty elapsed was $350 with a standard deviation of $100.