Transport back in time before automobiles & roads, trains & railroad tracks, and airplanes existed. A message must be delivered on foot across the Sahara Desert from Casablanca to Marrakesh. One person can carry enough food and water to last four days of traveling. The total journey requires six days. What is the minimum number of people that must start on the journey together in order for at least one person to to make it to Marrakesh while leaving nobody stranded in the desert without food or water? Explain your reasoning please.