4. Three recent college graduates have formed a partnership and have opened an advertising firm. Their first proiect consists of activities listed in the following table. Suppose it is now the end of the sixth day and that activities A and B have been completed, while activity D is 50 percent completed. Time estimates for the completion of activity D are 5,6 , and 7 . Activities C and H are ready to begin. 4a. (14 points) Determine the probability of finishing the project by day 21. 4b. (14 points) The partners have decided that shortening the project by two days would be beneficial, as long as it doesn't cost more than about $20,000. They have estimated the daily crashing costs for each activity in thousands, as shown in the following table. What is the minimum cost for shortening the project for two days and which activities should be crashed