Answer:
How do you represent selling 6 copies as an integer? With -6
How do you represent receiving 24 books as an integer? With 24.
Explanation:
The important thing to state here is what is the thing that you are counting.
If you count the number of copies/books that you have, then:
Selling 6 copies means that you have 6 copies less than before, then you would represent this with a -6.
"-6 copies"
And receiving 24 books means that you have 24 books more than before, then you will represent this with a +24.
"24 books"
(You do not need to write the "+" sign, it is implicit if you don't write any sign)