4. Sgwrs Ltd. is a firm based in Cardiff that produces mobile phones. The production manager, Bronwyn Jones, has developed the following chart that breaks down the production process into fifteen operations, and provides the immediate predecessors of each operation and each operation time in minutes. Immediate Operation Predecessors Time (mins.) Operation 1 none 6 2 1 3 3 2 9 4 2 5 5 3 8 6 2 10 7 4 7 8 4 4 9 5,6 9 10 6,7 8 11 8 4 12 9 12 13 11 7 14 10, 12 3 15 13, 14 5 Bronwyn informs you to assume a cycle time of 30 minutes. (a) Determine the minimum number of stations that could be achieved, and use the ranked positional weights technique to achieve a balance for this number of stations. (b) Is there a solution with the same number of stations you used above, but with a lower cycle time? If so, what is the minimum cycle time that gives a balance with the same number of stations you found above? (c) For three stations, find a balance with the smallest possible cycle time.