Tanker Scheduling Problem, solve as a Linear Programming

A shipline company requires a fleet of ships to service requirements for carrying

cargo between six cities. There are four specific routes that must be served

daily. These routes and the number of ships required for each route are as

follows:

All cargo is compatible, and therefore only one type of ship is needed. The

travel time matrix between the various cities is shown.

It takes one day to off$-$load and one day to on$-$load each ship. How many ships

must the shipline company purchase?