Answer: The description of the box plot is below.
First, the ends of the box plot should be just before 20 and past 40. If most of the values are between 20 and 40, the ends of the box plot should be just outside of those.
Second, the inner box of the box plot should definitely be between 20 and 40. The box contains 50% of the values, we would want this inside the given range of 20 to 40.