Can someone show me how to do this problem? steps with explanations please

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Kelle Carpet and Trim installs carpet in commercial offices. Peter Kelle has been very concerned with the amount of time it took to complete several recent jobs. Some of his workers are very unreliable. A list of activities and their optimistic completion time, the most likely completion time, and the pessimistic completion time (all in days) for a new contract are given in the following table: Time (days) b Immediate Predecessor(s) Activity a m 7 8 3 10 11 3 8 12 4 9 7 13 5 Y 9 2 7 3 7 1 5 11 15 4 B, D A, E A, E F 3 9 13 G 12 17 8 19 12 HT This exercise contains only part a. a) Based on the activity time estimates, the expected times and variance for each of the activities are: (Round your responses to two decimal places.) a) Based on the activity time estimates, the expected times and variance for each of the activities are: (Round your responses to two decimal places.) Activity Expected Time Variance A B C D E F G H I J K