A quality control engineer is interested in the mean length of sheet insulation being cut automatically by machine. The desired mean length of the insulation is 12 feet. It is known that the standard deviation in the cutting length is 0.15 feet. A sample of 70 cut sheets yields a mean length of 12.14 feet. This sample will be used to obtain a 95% confidence interval for the mean length cut by machine. The critical value to use in obtaining the confidence interval is 1) 1.96 2) 2.649 3) 2.58 4) 1.645