The following observations are amounts of hydrocarbon emissions resulting from road wear of bias-belted tires under a 522 kg load inflated at 228 kPa and driven at 64 km/hr for 6 hours ("Characterization of Tire Emissions Using an Indoor Test Facility," Rubber Chemistry and Technology, 1978: 7-25): .045, .117, .062, and .072. What confidence levels are achievable for this sample size using the signed-rank interval? Select an appropriate confidence level and compute the interval.