A random sample of 40 rolls of 5/16 inch diameter aircraft cable was taken from current production of the Calamity Cable Company. A piece was selected from each roll and fastened into a mechanical stretcher which could read the force which broke the cable. The mean of the 40 samples was 517 pounds with a sample standard deviation of 44 pounds. What is the 90 % confidence level of the true mean, m, of the breaking strength of that kind of cable?