Hey there!
Here is your answer:
The proper answer to this question is "9 pounds".
Reason:
Just add....
2.40=3 pounds
2.40
+
2.40
____
4.80
+
2.40
____
7.20
Therefore you would be able to buy 9 pounds of apples with 80 cents left!
If you need anymore help feel free to ask me!
Hope this helps!
~Nonportrit