Minimization of idle time with two kinds of actors
Observe that it takes a PM about 75 times as long to produce a widget as it takes a TM to clear that widget and let it start producing the next widget. And we have only 5 PMs.

Intuitively, it seems like we should have only one TM. It will be idle almost all the time, waiting for one of the PMs to finish. The PMs will be busy almost all the time, except right after they finish a widget and have to wait for the output to be cleared away.

Adding more TMs would simply add more idle time for them, while reducing the PM idle time by very little at best. Removing the sole TM would leave all of the PMs idle as soon as each of them finishes the first widget.

If the times were more similar, or the number of PMs were closer to 75, finding the answer would be more complex. This problem seems to be designed for a simple, intuitive answer.