Answer:
Based on the information given in the box plot, the appropriate measure of center for the data is the median, and its value is 19.
The median is the middle value of the dataset when the values are arranged in order from lowest to highest. In this case, the box extends from 17 to 20 on the number line, and the line in the box is at 19. This indicates that half of the data falls below 19 and half of the data falls above 19.
Therefore, the median value of the number of tickets sold for the dance is 19, and it is the best measure of center for this dataset.
The correct answer is: The median is the best measure of center, and it equals 19.