Hospital workers who are routinely involved administrative radioactive tracer to patients are subject to a radiation exposure emanating from skin of the patient. In an experiment to asses the amount of this , radiation levels were measured at a distance of 50 cm from n=28 patients who had been injected with a radioactive tracer , and a sample mean of 5.145 and sample std. s= 0.7524 are obtained. Can we be confident that the average radiation level at a 50 cm distance from patient is no more than about 5.5?