The quality control manager at a light bulb factory needs to estimate the mean life of a large shipment of light bulbs. The standard deviation is 72 hours. A random sample of 36 light bulbs indicated a sample mean life of 260 hours, Complete parts (a) through (d) below a. Construct a 99% confidence interval estimate for the population mean life of light bulbs in this shipment The 99% confidence interval estimate is from a lower limit of hours to an upper limit of hours. (Round to one decimal place as needed.)