3. Consider results of 20 randomly chosen people who have run a marathon. Their times, in minutes, are as follows: 137, 146, 150, 163, 166, 179, 186, 193, 196, 213, 218, 225, 236, 239, 254, 269, 271, 279, 282, 295. Calculate a 90% upper confidence bound on the mean time of the race. Assume distribution to be normal. Hint: the population variance is known or unknown