Please explain

The critical activities are the activities worth 0 slack which are A,B,C,E,G,H And because of that the project manager should track these critical activities most closely. Below is information about a project to implement a new manufacturing cell to assemble personal digital assistant devices. Assume 5-day week. Duration Task Immediate Estimates Predecessors A Determine process requirements 2 weeks None B. Benchmark competitor's processes 4 weeks A C. Prepare benchmark report 1 week B D. Design process and layout (preliminary) 2 weeks A E. Finalize design and set up manufacturing cell 2 weeks C&D F. Select and train operators 1 week G. Pilot test new process 2 weeks E&F D 1 week G H. Finalize process design Draw an activity on node (AON) network and Identify the Early start, Early Finish, Late Start, Late finish, critical Path, Total float and free float using the critical path algorithm, point, critical path, -1 point, total float and free float -1 point = 6 points. In the end what would happen if a new estimate for Task D increases its expected duration from two weeks to six weeks? Would the project take longer or would anything else change