Tammy bought 24 apples to feed her horse. She wants to give her horse 2 apples a day. Tammy said that after 10 days she will have 4apples left. Is she correct

Yes she is correct ...

the reason why is because if she gives her horse 2 apples a day for 10 days, she will have spent 20 apples.

and so to get the number of apples she has remaining after 10 days, just subtract 20 from 24:

24-20 = 4

and you get four. That means that after 10 days she will indeed have 4 apples left