a) Network diagram is following: b) Gantt chart based on early start time is following: Resource histogram is following: In the above resource histogram, we see that there is resource overload in periods 3 to 9 This resource overload can be removed by rescheduling activity C to start from period 9 Resulting Gantt chart is following: Resource histogram is following: We see that project completion time remains unchanged before and after resource leveling. Project completion time = 30