A shipping company operates 10 container ships that can each

A shipping company operates 10 container ships that can each carry 5,000 containers on each journey between ports. They want to be able to load and unload 20,000 containers each week. Assume their ships always travel fully loaded. What is the longest average travel time between ports that allows them to meet their foal of 20,000 containers per week? (Hint: the flow unit is a container)