An article presents a study of the effect of the subbase thickness on the amount of surface deflection caused by aircraft landing on an airport runway. in six applications of a 160 kn load on a runway with a subbase thickness of 864 mm, the average surface deflection was 2.34 mm with a standard deviation of 0.090 mm. find a 90% confidence interval for the mean deflection caused by a 160 kn load. round the answers to three decimal places.