9,9,10,10,10,10,12,12,12,12,12,12,12,13,13,13,13,13,13,14,14,14,14,14,14,14,14,14,14,15,15,15,15,15,15,15,18,18,18,18,19,19,20,22,22,23,23,24

In creating a histogram or frequency polygon for these data, what would the class interval be?

What percentage of items circulate between 11.06 and 15.57 days?

If these sample items represent the population and the lending period was reduced from 21 to 14 days, what percent of the circulation would be impacted?