Answer: 0.6 (choice B)
x = number of days the book has been checked out
Check out the attached image below. I've marked 3 boxes in red to represent the bars that span from x = 9 to x = 18. The heights of these bars add up to 0.15+0.30+0.15 = 0.45+0.15 = 0.60
So if we randomly pull out a book, then the chances of picking a book that has a x value between 9 and 18 (including 9; excluding 18) is 0.60
