A design ervgineer wants to construct a sample mean chart for controlling the service life of one of the types of Hight buibs his company produces. He knows from numerous previous sampies that this service life is nomally distributed with a mean of 500 hours and a standard deviation of 20 hours, On three recent production batches. the tested service life on randorn samples of four bulbs, with these results! In use useper and lower control Himits of 520 and 480 hours, 01 what samplets) (if any) does service tife appear is be out of contral? Show the reguired conputations to earn foll credit