Three inmates escorted by three guards to be transported by boat from the mainland to a penitentiary island to serve their sentences. The boat transfers no more than two persons in either direction. The inmates are certain to overpower the guards if they outnumber them anywhere at any time. Assume for simplicity that a shuttle trip in either direction can be operated entirely by inmates where constant area patrol precludes escape attempts. Develop a network model that determines the boat trips in a manner that ensures the safety for the guards.