CCSS IP Math II 3.5.1 Example 3

Moe and Marco deliver a regular order to a specialty foods store. Moe can unload the truck in minutes if he works alone. Moe and Marco can unload the truck in minutes if they work together. How many minutes does it take Marco to unload the truck if he works alone? Assume both men work at steady rates and their rates are not affected by either working alone or working together.