I have a question on D. How do you know what the maximum weeks a project can be crashed. The critical path is 16 weeks, the next path is 12 weeks. I am sure where 7 comes from. Can someone explain the math behind this?

Development of Version 2.0 of a particular accounting software product is being considered by Jose Noguera's technologiy firm in Baton Rouge. The activities necessary for the completion of this project are listed in the following table: a) Based on the given information regarding the activities for the project, the project length = weeks. b) The total cost required for completing this project on normal time =$ c) For reducing the duration of the project by one week, the activity that should be crashed first is activity The cost of the project based on the first activity selected for crashing will increase by $ d) The maximum weeks by which the project can be reduced by crashing = weeks. Total cost of crashing the project to minimum (or maximum weeks possible) =$