Costs are rising for all kinds of medical care. the mean monthly rent at assisted-living facilities was reported to have increased 17% over the last five years to $3486 (the wall street journal, october 27, 2012). assume this cost estimate is based on a sample of 120 facilities and, from past studies, it can be assumed that the population standard deviation is s = $650. a. develop a 90% confidence interval estimate of the population mean monthly rent. b. develop a 95% confidence interval estimate of the population mean monthly rent. c. develop a 99% confidence interval estimate of the population mean monthly rent. d. what happens to the width of the confidence interval as the confidence level is increased? does this seem reasonable? explain.