### Puzzle 55
Yes, 1 way (which the Petri net illustrates).

### Puzzle 56
7 months.

### Puzzle 57
Only task E can take longer, up to 1 month.

Side note: I've had to look at too many PERT charts and am presently in PERT hell thanks to an ill-timed remark in a meeting on my part. Never suggest you know more about management than management (even when it's true). They may try to recruit you.