please explain the answer to section D for this question. Tell me why you are doing what you are doing?

13.23 The Memorial Hospital is creating a new patient-focused care system by redesigning a floor of the existing facility. The change involves changes in information systems, nurse responsibilities, various policies, and equipment. In sum, six major tasks must be undertaken. A PERT network diagram of the project, as well as optimistic, most likely, and pessimistic times (in weeks) for each activity are estimated and given in Figure EX 13.23 and Table EX 13.23.1. D Start Finish Figure EX 13.23 Table EX 13.23.1 Weekly Compression Cost ($) Optimistic Pessimistic Activity A B Most Likely 3 Cost of Activity 50 25 1 1 1 40 C 2 40 40 D 4.5 5 8 100 30 E 1.5 2 5 70 90 F 5 7 90 70 -= Activity cannot be compressed. c. a. What is the total project completion time (in weeks), and which path is critical? b. What does it cost to complete this project? What is the probability that the transformation will take more than ten weeks? (Hint: No consideration is given to cost; illustrate with three normal curves as in the text examples, and compute the joint probability to justify your answer.) d. If the profit opportunity for each week that the project is completed early is $60, how many weeks earlier should the project be completed (how many weeks should we crash) to minimize the total costs of the project? (Hint: Use Table EX 13.23.2 to show your work; total costs of completing the project include both profit opportu- nity and direct cost and cumulative crashing costs.) Table EX 13.23.2 (7)=(6) -(5) (1) (2) (3) (4) (5) Total Cost of Cumulative Compressed Weeks for Compressed Compression Compression Cost Weeks Completion Activities (5) ($) 0 8 7 (6) Cumulative Profit Opportunity Net Benefit 2 6 5