8. Scott DeWitte has laid out the major steps involved in the wing assembly process for an experimental aircraft. The activities are labeled A through D in the following table, which also shows their estimated completion times (in weeks) and immediate predecessors. An activity network diagram for this project is shown below. Immediate Time Estimates (weeks) Activity Predecessor(s) Optimistic (a) Most Likely (m) Pessimistic (b) A 4 18 B. ( 10 Start D a. For each activity, compute the expected completion time and the variance of the completion time. (Show work/explain reasoning to receive full credit.) b. What is the critical path for this project? Very briefly explain/justify. (Note: You do not need to show the ES, EF, etc.) c. What is the expected completion time of this project? What is the variance? (Show work/explain reasoning to receive full credit.) d. What is the probability that the project will take more than 20 weeks? (Show work/explain reasoning to receive full credit.)