<em>15 Books.</em>
<em>Look here this well help you understand.</em>
<em>Books: 3, 6, 9, 12, 15.</em>
<em>Passes: 2, 4, 6, 8, 10.</em>
<em>Since Jackson would get 2 Passes for 3 Books, you could just add 3 onto three, and add 2 onto 2 for each 3 books you add on the total of books.</em>
<em>Hope this helps and have a nice day.</em>
<em>-R3TR0 Z3R0</em>