41. A professor has 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 she spends walking to and from the building and between each errand. Suppose the Xi s are independent, normally distributed, with the following means and standard deviations:

m1  15, s1  4, m2  5, s2  1, m3  8, s3  2, m412, s43. She plans to leave her of ce at precisely 10:00 a.m. and wishes to post a note on her door that reads, I will return by t a.m. What time t should she write down if she wants the probability of her arriving after t to be .01?