One biochemical measure of bone resorption is tartrate-resistant acid phosphatase (TRAP), which can be measured in blood. In a study of bone turnover in young women, serum TRAPmeasured in 31subjects.The mean was 13.2 units per liter (U/l). Assume that the standard deviation is known to be 6.5 U/l. Find the sample size required to provide an estimate of the mean TRAP with a margin of error of 1.5 U/l for 95% confidence.