Answer:
11 Cards.
Explanation:
The stack has 24 cards. Cate added 8 cards. 24 + 8 = 32.
Elena then took 12 cards. In other words, 32 - 12 = 20.
Finally, Cate took 9 cards from the stack. 20 - 9 = 11. So the resulting amount of cards in the stack is 11.