The adventures of captain underpants.  The first epic novel

The captain underpants extra crunchy book o fun (2 copies)

And the Perilous plot of professor poopypants

extra crunchy book of fun 2

and the attack of the talking toilets

and the invastion of the incredibly naughty cafeteria ladies from outer space........

7 books for 4 credits.  or if you don't want the duplicate book 6 for 3.  plus pick another free book from tower