Since he bought 2.25 pounds, you multiply that by 1.6 to get a sum of 3.6. Since he paid with a ten dollar bill, and he only has to pay 3.60, they will give him back 6.40 in change.
48 books divided by 7 books per box. So since 7 can go into 48 6 times to make 42, the remainder is 6 books are left out. 6 boxes are filled. I interpreted the remainder by subtracting 42 from 48. And that's all I did. :)
I hope you like this answer and have a good night! :D
