Latisha's great aunt Zelda, who lives somewhere tropical, has been tasked with giving plant food (fertilizer) to a rare and valuable flower. The plant food is in seven different containers and has different concentrations and pH balance. Great Aunt Zelda must start this task today and give the plant its food one container per day in a specific order on seven different days.

Great Aunt Zelda has decided to label each container to help her remember the order.

She doesn't want to waste any of her precious labels. They are very dear to her for some reason. How many labels does she have to use if she wants to keep track of the correct order?