Little Billie has decided to earn some money over the summer, so she sets up a lemonade stand. She initially sets the price per cup low and sees good sales. Billie decides to greatly increase the price per cup on the second day, but sees her sales drop. In order to figure out the "sweet spot" for sales, Billie runs an experiment in which she changes the price for a cup of her lemonade each day and records the sales?