I have three errands to take care of in the Administration Building. Let Xi = the time t...

I have three errands to take care of in the Administration Building. Let X_i = 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: 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?