A manager wants to assign tasks to workstations as efficiently as possible and achieve an hourly output of four units. The department uses a working time of $56$ minutes per hour. Assign the tasks shown in the accompanying precedence diagram $($times are in minutes$)$ to workstations using the following rules:

a$.$ In order of most following tasks. Tiebreaker: greatest positional weight.

b$.$ In order of greatest positional weight. Tiebreaker: most following tasks.

c$.$ What is the efficiency?