The box plot represents the number of tickets sold for a school dance. A horizontal line labeled Number of Tickets sold that starts at 7, with tick marks every one unit up to 32. The graph is titled Tickets Sold for A Dance. The box extends from 15 to 21 on the number line. A line in the box is at 19. The lines outside the box end at 8 and 31. Which of the following is the appropriate measure of variability for the data, and what is its value?