Suppose we are interested in the mean speed of vehicles on interstate highways in the U.S. We checked the speed of 40 cars near exit 115 on the I-45 and the result is as below (in mph): 80, 75, 65, 70, 73, 72, 79, 73, 75, 77, 80, 75, 65, 70, 73, 72, 79, 73, 75, 77, 80, 75, 65, 70, 73, 72, 79, 73, 75, 77, 80, 75, 65, 70, 73, 72, 79, 73, 75, 77. Find the lower bound of a 95% confidence interval for the proportion of cars that are over 75 mph of speed on interstate highways in the U.S. (Answer in 5 decimals.)