A physician would like to know the mean fasting blood glucose value (milligrams per 100 ml) of patients seen in a diabetic clinic over the past 10 years. Determine the number of patient records the physician should examine in order to be 95% confident that the sample mean does not differ by more than 4 units from the population mean, with 90% power of the statistical test, and prior evidence from a pilot study that found a variance estimate of 64.