Answer:
3 to 4 books
Explanation:
OKay so since you already know that the kid spent 10.50 on books and he bough a book for 3.50 and some new for 3 dollars all you need to find is the equation on how many well lets see.
First start by calculating it you need to do addition on this.
Do 3.50 then add 3.50 which gives you 7 then add on 3.50 more to make the 10.50