An established method of analysis for chlorinated hydrocarbons in an air sample has a mean of 12.5 mg/m 3 and a standard deviation of 0.030mg/m 3 . (1)Calculate the 95% confidence interval of mean of four measurements obtained by this method. (2)How many measurements should be made if the 95% confidence interval of mean is to be 12.5mg/m 3 ±0.017mg/m 3 .