The number of people owing books more than 20 but less than 60 is

Per the official key, the bar representing readers with books strictly between 20 and 60 corresponds to the 20-40 class with 16 people.

Note: The phrasing is ambiguous; a stricter reading (20-40 plus 40-60) would give 16 + 14 = 30. We have followed the official answer of 16.