I have three errands to take care of in the Administration Building. Let Xi = the time that it takes for the ith errand (i = 1, 2, 3), and let X4 = the total time in minutes that I spend walking to and from the building and between each errand. Suppose the Xi's are independent, and normally distributed, with the following means and standard deviations: µ1 = 15, σ1 = 4, µ2 = 5, σ2 = 1, µ3 = 8, σ3 = 2, µ4 = 12, σ4 = 3. I plan to leave my office at precisely 10:00 a.m. and wish to post a note on my door that reads, "I will return by t a.m." What time t should I write down if I want the probability of my arriving after t to be .01?